Question 71·Medium·Equivalent Expressions
Which expression is equivalent to ?
For polynomial equivalence questions, work methodically: first expand any binomials using FOIL or known patterns like , then distribute any outside coefficients, and finally combine like terms. Pay special attention to minus signs in front of parentheses—rewrite subtraction as adding the opposite (distribute the negative to every term) before combining terms. If you’re unsure, you can quickly plug in a simple value of (such as or ) into both the original and each choice to eliminate clearly wrong options, then finish the algebra to confirm the exact match.
Hints
Identify the two parts
Separate the expression into its two main parts: and . Think about how you usually expand a squared binomial and a product of two binomials.
Handle the square first
Focus on . Use FOIL or the pattern , then remember you still need to multiply the result by 2.
Expand the second product carefully
For , multiply each term in the first parentheses by each term in the second, then combine like terms.
Be careful with the minus sign
When you compute , remember that the minus sign applies to every term in the second parentheses before you combine like terms.
Desmos Guide
Enter the original expression as a function
In Desmos, type f(x) = 2(3x - 5)^2 - (x - 7)(6x + 2) so you have the original expression represented as a graph or function.
Enter each answer choice for comparison
Type each option as a separate function, for example: g(x) = 12x^2 - 100x + 64, h(x) = 12x^2 - 20x - 64, p(x) = 18x^2 - 20x + 64, and q(x) = 12x^2 - 20x + 64 (or similar labels).
Compare graphs or values
Look at the graphs: the function whose graph exactly overlaps with for all visible is the equivalent expression. You can also create a table for several -values (like ) and check which option always gives the same outputs as .
Step-by-step Explanation
Expand the squared binomial
Start with the first part: .
Expand using FOIL or the pattern :
Distribute the 2 across the trinomial
Now multiply the result by 2:
So the first part simplifies to .
Expand the product
Use FOIL on :
- First:
- Outer:
- Inner:
- Last:
Combine like terms:
Subtract the second trinomial and combine like terms
The full expression is
Substitute the simplified forms:
Distribute the minus sign across the second parentheses:
Now combine like terms:
So the simplified expression is , which matches choice D.