Question

Factor f(x) = 4x3 + 15x2 – 24x + 5 into linear factors given that - 5 is a zero of f(x).15f(x) = 4x3 + 15x2 - 24x + 5 =(Factor completely.)

Answer 1

If x=-5 is a zero, then the first factor of the polynomial would be (x + 5 )

To find the other two factors we can divide the polynomial by the expression (x+5).

Using synthetic division, we have:

-5 I 4 15 -24 5 (Coefficients of the dividend)

I -20 25 -5 (Multiplying each coefficient by the results of the substraction and adding)

-----------------------------------------------------------------------------------

4 -5 1 0 (Coefficients of the quotient)

The result of the division is 4x^2 - 5x + 1. Factoring it, we have:

4x^2 - 4x -x + 1 (Separating -5x into -x and -4x)

4x (x - 1) - (x -1) (Factoring each pair of terms)

(x-1)(4x-1) (Factoring using the common factor)

So the answer would be:

(x + 5 )(x-1)(4x-1)