Best Digital SAT Math Prep: "Equivalent Expressions"
Frontier Lesson: "Equivalent Expressions" for the Digital SAT
"Equivalent Expressions" is a skill that falls under the "Advanced Math" domain. While it may sound intimidating at first, it's actually one of the more manageable parts of the SAT math section. By focusing on basic rules of algebra and key strategies for simplifying or rewriting expressions, you can confidently solve these problems.
Essentially, "equivalent expressions" refers to the process of rewriting a mathematical expression into another form that has the same value for all valid inputs. Unlike some other problem types on the SAT, questions in this topic do not involve solving equations or finding the value of variables. Instead, the task is simpler: transform or rearrange the given mathematical expression into an equivalent form. The question prompt often starts with "Which expression is equivalent to...," making it clear that the goal is to modify the expression without altering its meaning.
On the SAT, most "Equivalent Expressions" questions are presented in multiple-choice format, offering four possible answer choices. This is good news! Having pre-set answers means you can often verify your work quickly and confirm whether you've chosen the correct form.
In terms of difficulty, the majority of these problems fall within the easy to moderate range, meaning they are very approachable for well-prepared students. Even the "hard" questions in this category are rarely very difficult. A strong understanding of techniques like factoring, expanding, and simplifying polynomials will allow you to consistently earn points here.
π― The "Equivalent Expressions" questions reward precision and mastery of basic algebraic manipulation techniques, such as:
Applying the distributive property
Factoring polynomials (e.g., difference of squares, grouping, or common factors)
Combining like terms
Simplify rational expressions
How to Factor Quadratic and Polynomial Expressions?
Factoring quadratic expressions is a fundamental skill when tackling "Equivalent Expressions" problems on the SAT. In this section, we'll break down the essential steps and techniques to factor quadratics effectively.
π Step 1: If possible, reduce the coefficient of x2 to 1
Before factoring, try to simplify the equation by factoring out the greatest common factor (GCF) of all the terms. For example:
Given the quadratic 5x2β10x+25, notice that 5 is a common factor for all terms. Factor out 5:
5x2β10x+25=5(x2β2x+5)
Now, focus on factoring x2β2x+5 within the parentheses.
π― Key Insight: In many SAT problems, you may encounter quadratics where the coefficient of x2 cannot be easily reduced. In those cases, you will factor directly (covered below). Always look out for common factors first as they simplify the processβbut they are not always present.
π Step 2a: Factor x2+bx+c (when the coefficient of x2=1)
When the coefficient of x2 is 1, factor by finding two numbers that:
Multiply to c (the constant term), and
Add to b (the coefficient of x).
Example: Factor x2+5x+6:
The constant term is c=6. The coefficient of x is b=5.
Find two numbers that multiply to 6 and add to 5:
These numbers are 2 and 3, because 2Γ3=6 and 2+3=5.
So:
x2+5x+6=(x+2)(x+3)
π Step 2b: Factor ax2+bx+c (when the coefficient of x2 is not 1)
When the coefficient of x2, a, is not 1, use the grouping method for factoring.
Multiply aβ c.
Find two numbers that:
Multiply to aβ c, and
Add to b.
Rewrite bx as the sum of two terms using these values, and group terms in pairs.
Factor out the greatest common factor (GCF) from each group.
Rewrite as a product of two binomials.
Example: Factor 6x2+11x+4:
Multiply aβ c=6β 4=24.
Find two numbers that multiply to 24 and add to 11: These are 8 and 3.
Rewrite 11x as 8x+3x:
6x2+11x+4=6x2+8x+3x+4
Group terms:
(6x2+8x)+(3x+4)
Factor out the GCF from each group:
2x(3x+4)+1(3x+4)
Rewrite as:
(2x+1)(3x+4)
π― Tip: Practice recognizing the numbers that fit the criteria for both factoring b and grouping. Mastery here is key for efficiency on the SAT!
π Special Factoring Rules
Some expressions are easier to factor because they follow special patterns. Knowing these rules will save you time and effort on the test. Let's review and break down the most common types.
β€ (a) Square of a Sum
a2+2ab+b2=(a+b)2
The first term is a perfect square, a2.
The last term is also a perfect square, b2.
The middle term must equal 2ab.
Example:
Factor x2+6x+9:
Identify a=x and b=3 (32=9).
Verify 6x=2ab=2(x)(3).
Rewrite as:
x2+6x+9=(x+3)2
β€ (b) Square of a Difference
a2β2ab+b2=(aβb)2
Similar to the square of a sum, except the middle term has β2ab.
Example:
Factor 4x2β12x+9:
Identify a=2x and b=3 (32=9, (2x)2=4x2).
Verify β12x=β2(2x)(3).
Rewrite as:
4x2β12x+9=(2xβ3)2
β€ (c) Difference of Squares
a2βb2=(a+b)(aβb)
This applies when an expression contains the difference of two perfect squares.
Example:
Factor x2β16:
Identify a=x and b=4 (42=16).
Rewrite as:
x2β16=(x+4)(xβ4)
Example 2:
Factor 9x2β25y2:
Recognize both 9x2=(3x)2 and 25y2=(5y)2.
Rewrite as:
9x2β25y2=(3x+5y)(3xβ5y)
π― Tip: Always check if an expression is a difference of squares, as this is a common pattern tested on the SAT.
β€ Final Steps for Factoring Quadratics
Factor out common terms first. Simplify whenever possible.
Recognize patterns. Identify if the quadratic fits special factoring forms.
Test your work. Multiply your binomials back to verify equivalence.
Watch for SAT traps. Be cautious of answer choices that seem correct but don't fully simplify.
π Common Integer Square Table
Memorize them and enhance your sensitivity to the square and root of numbers, which is very useful for increasing your problem-solving speed and efficiency in real SAT.
Single-digit Integers and Their Squares
Integers Between 10 and 20 and Their Squares
1Γ1=1
10Γ10=100
2Γ2=4
11Γ11=121
3Γ3=9
12Γ12=144
4Γ4=16
13Γ13=169
5Γ5=25
14Γ14=196
6Γ6=36
15Γ15=225
7Γ7=49
16Γ16=256
8Γ8=64
17Γ17=289
9Γ9=81
18Γ18=324
19Γ19=361
20Γ20=400
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Exponential Expressions & Operations with Polynomials
π Common Types of Polynomials in SAT Questions:
A polynomial is an expression consisting of one or more terms. Each term may include a coefficient, a variable base, and an exponent.
Monomial: A polynomial with a single term. Example: 5x3, β7y, 30
Binomial: A polynomial with two terms. Example: x2β3x, 5y+2, x3β11x2
Trinomial: A polynomial with three terms. Example: x2+2xβ1, 3y3β4y+6
π How to Add or Subtract Polynomials
Polynomials can be added or subtracted by combining like terms, sharing the same rules of exponent pperations.
β€ a. Combine Like Terms
Definition: "Like terms" share the same variable base AND the same exponent.
You can obly combine: Terms with matching variable bases and exponents. Example: 3x2+2x2=5x2
You cannot combine: Terms with different variable bases or exponents. Example: 3x3+5x2ξ =8x5 (cannot be simplified further).
Try: combine like terms to simplify 2x2β5x+3+4x2+6xβ1
Key: (2x2+4x2)+(β5x+6x)+(3β1)=6x2+x+2
β€ b. Combine Only the Coefficients
When combining like terms, only the coefficients change. The variable base and exponent remain the same.
For example:
4x3β7x3=(4β7)x3=β3x3
β€ c. Be Mindful of Parentheses and Signs
When adding or subtracting polynomials in parentheses, ensure that you correctly distribute any negative sign across terms.
Example 1:
Simplify (3x2+2xβ5)β(x2βx+4):
Distribute the negative sign:
(3x2+2xβ5)βx2+xβ4
Then combine like terms:
(3x2βx2)+(2x+x)+(β5β4)=2x2+3xβ9
β€ d. Write Expressions in Descending Order of Exponents
After combining terms, arrange polynomial terms in order from the highest power of the variable to the lowest.
Example: reorder 5xβx3β3+2x2:
βx3+2x2+5xβ3
π How to Multiply Polynomials
The process for multiplying polynomials involves distributing each term of one polynomial to all the terms of the other.
β€ a. Distribute Terms When Multiplying Polynomials
When multiplying two polynomials, multiply each term in one polynomial by each term in the other polynomial.
Example: Multiply 2x(3x+4):
2xβ 3x+2xβ 4=6x2+8x
β€ b. Use the FOIL Method for Binomials
When multiplying two binomials, you can use FOIL to systematically account for all four products:
(ax+b)(cx+d)
FOIL Steps:
F (First): Multiply the first terms: axβ cx=acx2
O (Outer): Multiply the outer terms: axβ d=adx
I (Inner): Multiply the inner terms: bβ cx=bcx
L (Last): Multiply the last terms: bβ d
**Then, combine the results. For example, for (2x+3)(xβ4):
First: 2xβ x=2x2
Outer: 2xβ (β4)=β8x
Inner: 3β x=3x
Last: 3β (β4)=β12
Final result:
2x2β8x+3xβ12=2x2β5xβ12
β€ c. Multiplying Terms with the Same Base
When multiplying terms that have the same base, apply these rules:
Multiply the coefficients.
Keep the base the same.
Add the exponents.
Example 1:
(2x3)(4x2)=(2β 4)x3+2=8x5
Example 2:
(5x2)(3)=(5β 3)x2=15x2
π― Tips: Always simplify your final expression and write the terms in descending order of exponents.
π What Is an Exponential Expression?
An exponential expression is any expression where a number or a variable is raised to a power (exponent).
Example: In the expression β2x5:
β2 is the coefficient (the numerical factor).
x is the base (the repeated factor).
5 is the exponent (the number of times the base is multiplied by itself).
Important Difference Between β2x5 and (β2x)5
β2x5: The exponent 5 applies only to x, so:
β2x5=β2(xβ xβ xβ xβ x)
(β2x)5: The entire expression (β2x) is raised to the 5th power, meaning both β2 and x are multiplied by themselves five times:
(β2x)5=(β2)5β x5=β32x5
π― Tip: Parentheses are critical! Always consider what the exponent applies to, and interpret expressions carefully!
π The Rules of Exponent Operations
For all the rules below, the base can represent either a number or a variable, and they apply the same way to integer or fractional (rational) exponents.
β€ a. Adding and Subtracting Exponential Expressions
You can add or subtract exponential expressions only if they have the same base with the same exponent.
Example:
3x2+5x2=8x27x3β2x3=5x3
You cannot combine terms with different exponents or bases:
Example: 4x2+3x3ξ =7x5 (it cannot be combined further).
β€ b. Multiplying Exponential Expressions
When multiplying exponential expressions with the same base, keep the base the same and add the exponents.
Rule:
amβ an=am+n
Example:
x3β x4=x3+4=x7
β€ c. Dividing Exponential Expressions
When dividing exponential expressions with the same base, keep the base the same and subtract the exponents (top exponent minus bottom exponent).
Rule:
anamβ=amβn,Β whereΒ aξ =0
Example 1:
x2x5β=x5β2=x3
Example 2:
If the terms have coefficients, divide the coefficients and apply the rule to the exponents:
4x38x6β=48ββ x3x6β=2x6β3=2x3
β€ d. Raising an Exponential Expression to an Exponent
When raising an exponential expression to another exponent, multiply the exponents.
Rule:
(am)n=amβ n
Examples:
(x3)4=x3β 4=x12(2x2)3=(23)(x2β 3)=8x6
β€ e. Negative Exponents
Negative exponents represent the reciprocal of the base raised to the corresponding positive exponent.
Rule:
aβn=an1β,Β forΒ aξ =0
Examples:
xβ3=x31β(2x)β2=(2x)21β=4x21β
β€ f. Zero Exponent
Any nonzero base raised to the power of zero equals 1.
Rule:
a0=1,Β forΒ aξ =0
Examples:
50=1,x0=1,(βy2)0=1,β8x0=β1
β€ g. Rewriting Roots as Rational Exponents
Radical expressions (roots) can be rewritten as rational (fractional) exponents. This is particularly helpful for simplifying expressions with roots.
Rule for Square Root:
xβ=x21β
Rule for Higher Roots:
nxmβ=xnmβ
Here:
m is the exponent under the radical (inside the root).
n is the root (the value to the left of β).
Examples:
Square root:
x3β=x23β
Cube root:
3x2β=x32β
General example:
4x5β=x45β
How to Do Operations with Rational Expressions
π What Are Rational Expressions?
A rational expression is a fraction where the numerator or denominator (or both) are polynomials. In other words, it represents the division of one polynomial by another.
Examples:
x1β,xβ1x2+2x+1β,x2β43xβ
Key Note:
The skills required for working with rational expressions (factoring, distributing, combining terms, etc.) are based on everything we've covered earlier about working with polynomial and exponential expressions.
π How to Simplify Rational Expressions
Simplifying rational expressions is similar to simplifying fractions: factor both the numerator and the denominator and cancel any common factors.
Steps to Simplify a Rational Expression:
Factor the numerator and denominator completely.
Cancel common factors that appear in both the numerator and the denominator.
Write the resulting expression.
Example: Simplify x+2x2β4β:
Factor the numerator: x2β4=(x+2)(xβ2)
Rewrite: x+2(x+2)(xβ2)β
Cancel the common factor (x+2):
x+2(x+2)(xβ2)β=xβ2,xξ =β2
β οΈ Important: Always state any values of the variable that would make the original denominator equal to zero as restrictions (here, xξ =β2).
π How to Add or Subtract Rational Expressions
Adding and subtracting rational expressions follows the same rules as fractions:
Make sure the denominators are the same (common denominator).
Add or subtract the numerators.
Simplify if possible.
When the denominators are different, you need to find a common denominator (usually the least common multiple, LCM). In most cases, multiplying the two denominators together is the simplest way to find this.
Example: Add x1β+x+12β:
Multiply the denominators: x(x+1)
Rewrite both fractions with the common denominator:
x1β=x(x+1)x+1β,x+12β=x(x+1)2xβ
Add the numerators:
x(x+1)x+1β+x(x+1)2xβ=x(x+1)(x+1)+2xβ
Simplify:
x(x+1)x+1+2xβ=x(x+1)3x+1β
Note: You cannot combine rational expressions until they have the same denominator. Carefully distribute and simplify when expanding numerators.
π How to Multiply or Divide Rational Expressions
Multiplication and division of rational expressions use the same rules as with fractions.
β€ a. Multiplying Rational Expressions
When multiplying two rational expressions:
Factor all terms in the numerators and denominators.
Multiply the numerators and denominators.
Cancel common factors.
Example: Multiply 3xx2+2xββ x+29xβ:
Factor the numerator and denominator where possible:
3xx(x+2)ββ x+29xβ
Multiply the fractions:
3xβ (x+2)x(x+2)β 9xβ
Cancel the common factors (x+2) and x:
39xβ=3x,xξ =0,xξ =β2
β€ b. Dividing Rational Expressions
Dividing one rational expression by another is equivalent to multiplying by the reciprocal:
BAβΓ·DCβ=BAββ CDβ
Example: Divide x+3xβΓ·x2x+1β:
Rewrite as multiplication by the reciprocal:
x+3xββ x+1x2β
Multiply:
(x+3)(x+1)xβ x2β=(x+3)(x+1)x3β
β€ c. Factor First to Simplify Multiplication and Division
It is almost always faster and cleaner to factor and cancel first before writing the expanded form of the expression.
Example: Simplify x2+3xx2β4ββ xβ23xβ:
Factor:
x(x+3)(x+2)(xβ2)ββ xβ23xβ
Cancel (xβ2) and x:
x+33(x+2)β,xξ =β2,xξ =0,xξ =β3
π How to Rewrite Rational Expressions as Quotients and Remainders
When the degree of the numerator is higher than or equal to the degree of the denominator, you can rewrite the rational expression in the form of a quotient and remainder:
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Common Traps & Tips in Digital SAT
β οΈ Common Traps
Incorrect distribution: Remember that a(b+c)=ab+ac, not a(b+c)=ab+c. For example, 3(x+2)=3x+6, not 3x+2.
Cancellation errors: When simplifying fractions like x+3x+5β, you cannot cancel the x terms. You can only cancel factors, not terms. For example, in (x+1)(x+1)(xβ1)β,xξ =β1, you can cancel (x+1) to get (xβ1).
Exponent confusion: Remember that (x+y)2ξ =x2+y2. The correct expansion is (x+y)2=x2+2xy+y2.
Factoring mistakes: Not all quadratics factor nicely. For example, x2+5x+3 cannot be factored using integer coefficients.
Domain restrictions: When simplifying rational expressions, always check for domain restrictions. For example, xβ2x2β4β=x+2 only when xξ =2.
π‘ Helpful Tips for the Digital SAT
Tip 1: Use the "Plug in Numbers" Strategy
When questions are in multiple-choice format, test the options by plugging in easy values for the variables (e.g., x=1, x=0, or x=β1), where valid.
Example: Simplify 16x3+7x2β(5x3β8x2+xβ6)
If unsure how to directly simplify, plug in x=1 into both the expression and the answer options.
Original expression: 16+7β(5β8+1β6)=31
Find correct answer option matching 31
Tip 2: Rewrite All Exponents and Roots as xm
Avoid working with radicals or fractions; instead, rewrite them in exponential form for easier manipulation.
For example: xββx1/2,x31ββxβ3
You can now use exponent rules more efficiently, such as: xaβ xb=xa+b,xbxaβ=xaβb
Quick Practice: Test Your Skills!
Question 1
Which expression is equivalent to 2a3(aβ1)+5a4β(a3β10) ?
A. 7a4β2a3+10
B. 7a4β3a3+10
C. 7a4β3a3β10
D. 7a4βa3+10
Solution:
Step 1: Expand the expression 2a3(aβ1)
Distribute 2a3 across (aβ1): 2a3(aβ1)=2a4β2a3
Step 2: Rewrite the full expression with the expansion
Or we can plug x=1 into the expressions to find out which option is true:
m=7β 1β5=2 and n=x2+2=12+2=3, so: mnβn=2β 3β3=3
Next, we plug x=1 into the given options:
For A: 7x3β5x2+14xβ12=4, which is ξ =3, so it's wrong.
For B: 7x3β6x2+14xβ8=7, which is ξ =3, so it's wrong.
For C: 7x3β6x2+14xβ12=3, which is =3, so it's possible to be true.
For D: 7x3β5x2β14xβ10=β22, which is ξ =3, so it's wrong.
Since only Option C matches 3, it's the correct answer.
Question 5
10x3β5x2β5x
The given expression is equivalent to ax(xβ1)(bx+1), where a and b are constants. What is the value of b?
Solution:
Step 1: Factor out the common term in the polynomial
The given polynomial 10x3β5x2β5x has 5x as a common factor. So, we factor it out:
10x3β5x2β5x=5x(2x2βxβ1)
Step 2: Factorize the quadratic 2x2βxβ1
Identify the coefficients:
a=2 (coefficient of x2)
b=β1 (coefficient of x)
c=β1 (constant term)
Find two numbers that multiply to aβ c=2β (β1)=β2 and add to b=β1:
The numbers are β2 and 1.
Split the middle term using these numbers:
2x2βxβ1=2x2β2x+xβ1
Group the terms in pairs and factorize:
(2x2β2x)+(xβ1)=2x(xβ1)+1(xβ1)
Factor out the common binomial (xβ1):
2x2βxβ1=(2x+1)(xβ1)
Step 3: Rewrite the full factorization
Substitute the factored quadratic (2x+1)(xβ1) back into the polynomial:
10x3β5x2β5x=5x(2x+1)(xβ1)
Step 4: Compare with the given form
The given form of the expression is:
From the factorization, we can identify:
a=5
b=2
Final Answer: The value of b is 2.
Your Turn! Realistic "Equivalent Expressions" Questions for DSAT Success
Question 1
Difficulty level: Easy
Which expression is equivalent to 158t3β24t2u?
A. 2t(79t2β12u)
B. 2t2(79tβ12u)
C. 2tu(79t2β12)
D. 2t2u(79tβ12)
Question 2
Difficulty level: Medium
The expression 72y5β48y4 is equivalent to ry4(12yβ8), where r is a constant. What is the value of r?
Question 3
Difficulty level: Hard
Which of the following expressions has a factor of x+2b, where b is a positive integer constant?
A. 2x2+5x+10b
B. 2x2+15x+10b
C. 2x2+20x+10b
D. 2x2+25x+10b
"Equivalent Expressions" Learning Checklist
π Master factoring ax2+bx+c
Always reduce the coefficient of x2 to 1 if possible.
Factor out common terms first. Simplify whenever possible.
Use the grouping method for factoring
π Memorize special factoring rules:
Square of a Sum a2+2ab+b2=(a+b)2
Square of a Difference a2β2ab+b2=(aβb)2
Difference of Squares a2βb2=(a+b)(aβb)
π Be familiar with the common integer square table.
π Understand what is an exponential expression: axm
π Be aware of the difference between axm and (ax)m
π Master the rules of exponent operations proficiently:
axm+bxm=(a+b)xm
axmβbxm=(aβb)xm
amβ an=am+n
anamβ=amβn, aξ =0
(am)n=amβ n
aβm=am1β, aξ =0
a0=1, aξ =0
namβ=anmβ
π Understand polynomials of different quantities of terms such as 5x2,x3βy2,x3βx+10
π Master how to add or subtract polynomials:
what are "like terms"
how to combine them(only the coefficients change)
π Master how to multiply polynomials:
Multiply each term in one polynomial by each term in the other polynomial, such as ax(x+b)=axβ x+axβ b
Use the FOIL method for binomials, (ax+b)(cx+d) = axβ cx+axβ d+bβ cx+bβ d
When multiplying terms that have the same base: multiply the coefficients, keep the base the same and add the exponents, such as: axmβ bxn=aβ bβ xm+n
π Master two core steps to simplify a rational expression:
Factor the numerator and denominator completely
Cancel common factors
π Master operations with rational expressions by using the same rules as fractions.
π Learn and practice polynomial long division to rewrite rational expressions as quotients and remainders: q(x)+b(x)r(x)β, where r(x) is the remainder.
π Making good use of the numerical substitution method, like x=0, x=1, to solve problems quickly, which is a very practical approach in real SAT.
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