Advanced MathMediumQuadratic left after cancelling cubes
Advanced Math practice question
For every value of x, the difference (x + 2)³ − x³ equals ax² + bx + c. What is the value of a?
Answer: 6
(x + 2)³ = x³ + 6x² + 12x + 8; subtracting x³ leaves 6x² + 12x + 8, so a = 6.
Common wrong answers
- If you answered 3
- The binomial coefficient 3 is multiplied by 2: the x² term of (x + 2)³ is 6x².
- If you answered 8
- 8 is c, the constant term 2³.
- If you answered 12
- 12 is b, the x-coefficient of the difference.
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