Question 113·Medium·Equivalent Expressions
Which of the following is equivalent to the expression above?
For algebraic equivalence questions, expand each part carefully using known patterns (like ) and the distributive property, then combine like terms while paying close attention to minus signs applied to entire parentheses. Simplify the expression step by step and only then look at the answer choices to match your result, rather than trying to manipulate the choices themselves, which saves time and reduces sign errors.
Hints
Separate the two parts
Think of the expression as two pieces: and , with a subtraction between them. Work out each piece separately before subtracting.
Use the square of a binomial pattern
For , recall the pattern . Identify and , then expand.
Be careful with the minus sign
After expanding , remember that the whole result is being subtracted. Distribute the negative sign to each term before combining like terms.
Desmos Guide
Define a value for y and enter the original expression
In Desmos, first set a value for , for example type y = 2. Then on the next line, type the original expression as a function of , such as f(x) = (2x + 5y)^2 - (x - y)(3x + 11y).
Enter each answer choice as a function
On new lines, enter each choice (using the same fixed value of ) as functions, for example g(x) = x^2 + 12x*y + 36y^2, h(x) = x^2 + 12x*y - 36y^2, etc. Use a table or the graph to compare these to .
Compare graphs or values to find the match
Check which choice’s function has exactly the same graph or the same table values as for many -values. The choice whose expression always matches the original expression is the correct answer.
Step-by-step Explanation
Expand the squared binomial
First expand using the pattern .
So the first part becomes .
Expand the product
Now expand by distributing each term in the first parentheses over the second.
So the second part is .
Subtract the second expression from the first
The original expression is
Substitute the expanded forms:
Be careful: the minus sign applies to every term inside the parentheses.
Distribute the negative and combine like terms
Distribute the negative sign across the second parentheses:
Now combine like terms:
- For : .
- For : .
- For : .
So the simplified expression is
which matches answer choice A.