Question 197·Medium·Equivalent Expressions
Which of the following is equivalent to ?
For expression-equivalence questions, first expand any parentheses by distributing all coefficients and negative signs, then combine like terms (group , , and constants). Work carefully with minus signs—especially when subtracting a whole parentheses—because most wrong choices come from sign mistakes. If you’re short on time or want a quick check, you can also plug in an easy value for (like or ) into the original expression and each answer choice; the correct choice will match the original for every value you try, while incorrect ones will differ.
Hints
Expand the first parentheses
Focus first on . Multiply 2 by each term inside the parentheses before doing anything with the second part.
Interpret the minus sign before the second parentheses
Think of as multiplying the whole parentheses by . How does that change the signs of each term inside?
Combine like terms carefully
Once both parentheses are expanded, group terms together, terms together, and constants together, and then add them.
Desmos Guide
Enter the original expression as a function
In Desmos, type f(x) = 2(3x^2 - 5x + 4) - (x^2 - 7x - 2) so you can compare every choice to this expression.
Enter each answer choice as separate functions
Type each option as its own function, for example:
g(x) = 7x^2 - 17x + 6h(x) = 5x^2 - 3x + 10p(x) = 5x^2 - 17x + 6q(x) = 7x^2 - 3x + 10Then use a table for each (click the gear icon, then the "+" and choose "table") to compare values of and each option at several -values (like ).
Decide which option is equivalent
Look for the function whose table values match for every you test; that function’s expression is the one equivalent to the original.
Step-by-step Explanation
Distribute the 2 over the first parentheses
Start by expanding .
Multiply each term inside the parentheses by 2:
So the first part becomes .
Handle the subtraction of the second parentheses
Now deal with .
A minus sign in front of parentheses means you multiply every term inside by :
So becomes .
Write the full expanded expression
Substitute the expanded pieces back into the original expression: becomes . Now you are adding two polynomials: and .
Combine like terms and match to a choice
Combine like terms:
- terms:
- terms:
- Constant terms:
So the simplified expression is , which matches answer choice B.