Advanced MathVery hardConstants in the factorisation of a sum of cubes
Advanced Math practice question
The polynomial x³ + 8 is equal to (x + 2)(x² + bx + c) for all x, where b and c are constants. What is the value of b + c?
Answer: 2
x³ + 8 = x³ + 2³ = (x + 2)(x² − 2x + 4). So b = −2, c = 4, and b + c = 2.
Common wrong answers
- If you answered 4
- 4 is c alone.
- If you answered 6
- 6 comes from b = +2.
- If you answered -6
- −6 comes from c = −4.
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