Question 81·Hard·Equivalent Expressions
The expression is equivalent to the expression , where , , and are constants.
What is the value of ?
(Express the answer as an integer)
For this type of SAT question, always expand products systematically and then combine like terms, watching signs carefully. Treat each binomial product separately using FOIL, rewrite the whole expression with parentheses, and distribute any minus signs before combining , , and constant terms. Finally, match the result to and read off the specific coefficient the question asks for, rather than fully focusing on all three coefficients if only one is needed.
Hints
Handle each product separately first
Start by expanding and one at a time using distribution (FOIL), rather than trying to do everything at once.
Be careful with the subtraction
Remember the entire second product is being subtracted. After you expand both products, put parentheses around the second one and distribute the minus sign to each of its terms.
Focus on the coefficient of
Once you have a single simplified expression, identify the term that has just (not and not the constant). Its coefficient is the value of .
Desmos Guide
Enter the full expression
In Desmos (graphing or scientific), type the entire expression exactly as given: (4x - 11)(9x + 2) - (5x + 13)(7x - 6).
Let Desmos simplify
Use Desmos’s simplify/expand feature (for example, on the scientific calculator, press the = button) so it outputs the equivalent polynomial in standard form .
Identify the coefficient of
From the simplified polynomial that Desmos shows, locate the term with just and note its coefficient; that value is .
Step-by-step Explanation
Expand the first product
Use distribution (FOIL) on :
- First:
- Outer:
- Inner:
- Last:
Combine like terms in the middle:
So becomes .
Expand the second product
Now expand in the same way:
- First:
- Outer:
- Inner:
- Last:
Combine like terms in the middle:
So becomes .
Subtract the second trinomial from the first
The original expression is
Substitute the expanded forms:
Distribute the minus sign across the second parentheses:
Now combine like terms:
- For terms:
- For terms:
- For constants:
Match to the form and state
From the combined terms, the simplified expression is
This matches with , , and . The question asks for , so the value of is .