Question 124·Easy·Equivalent Expressions
Which of the following expressions is equivalent to ?
For polynomial subtraction problems, first remove parentheses by distributing any minus sign across the second polynomial, changing the sign of each of its terms. Then neatly line up and combine like terms (squared terms, linear terms, constants) by adding their coefficients. To avoid sign mistakes under time pressure, say the new signs out loud in your head (“minus , plus , minus ”) and, if unsure, quickly check your result by plugging in an easy value like to see which answer choice matches the original expression.
Hints
Think about the subtraction
You are subtracting an entire polynomial. How does a minus sign in front of parentheses affect each term inside the parentheses?
Remove the parentheses
Rewrite the expression without parentheses by distributing the negative sign to each term of the second polynomial before combining anything.
Combine like terms
After distribution, group terms together, terms together, and constant terms together, and then add their coefficients.
Desmos Guide
Enter the original expression
In Desmos, type f(y) = (4y^2 + 3y - 2) - (y^2 - 5y + 6) to define the original expression as a function.
Enter each answer choice as a function
Define four more functions, for example: A(y) = 5y^2 - 2y + 4, B(y) = 3y^2 - 2y + 8, C(y) = 3y^2 + 8y - 8, and D(y) = 3y^2 + 8y + 8.
Compare graphs or use a table
Look at the graphs of and each choice; the equivalent expression will have a graph that lies exactly on top of for all visible -values. You can also create a table for and the choices at several -values (like ); the matching expression will give the same outputs as for every tested input.
Step-by-step Explanation
Rewrite the expression and identify the operation
Start with the given expression:
You are subtracting the entire second polynomial from the first, so the negative sign must apply to every term inside the second parentheses.
Distribute the negative sign
Distribute the minus sign to each term of the second polynomial:
- The becomes .
- The becomes .
- The becomes .
So the expression becomes:
Combine like terms carefully
Group like terms:
- terms:
- terms:
- Constant terms:
Now combine:
Write the simplified expression and match the choice
Putting the combined terms together, the simplified expression is:
This matches answer choice C, so is equivalent to the original expression.