Advanced MathMediumConstant after expanding a scaled difference of squares
Advanced Math practice question
When 2(x + 3)(x − 3) is written in the form ax² + c, where a and c are constants, what is the value of c?
Answer: -18 or −18
(x + 3)(x − 3) = x² − 9, so 2(x² − 9) = 2x² − 18. Thus c = −18.
Common wrong answers
- If you answered 9
- 9 is 3², with neither the sign nor the factor of 2 applied.
- If you answered 18
- 18 has the wrong sign.
- If you answered -9
- −9 forgets to multiply the constant by 2.
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