Question

If 5 is a zero of x³- 3x² - kx+15, find k.

Answer 1

Let x³-3x²-kx+15 be a f(x)

Since 5 is a zero of the polynomial, f(5)=0

This means,

5³-3×5²-5×k+15=0

125-75-5k+15=0

125-60=5k

65=5k

Divide both sides by 5

k=13