The zeros of a cubic polynomial function P are 1,√5, -√5. If P(x)=x^3+bx^2+cx+d, the P(2) is equal to?

Question

The zeros of a cubic polynomial function P are 1,√5, -√5. If P(x)=x^3+bx^2+cx+d, the P(2) is equal to?

Answer 1

From the given form for P(x), you can see that the leading coefficient is 1, so

P(x) = (x - 1)(x - √5)(x + √5) = (x - 1)(x² - 5)

P(2) = (2 - 1)(2² - 5) = -1

Answer 2

From the given form for P(x), you can see that the leading coefficient is 1, so

P(x) = (x - 1)(x - √5)(x + √5) = (x - 1)(x² - 5)

P(2) = (2 - 1)(2² - 5) = -1