16Hit1600
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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