Question

if x+1 is factor of ax³+x²+4a-9, find value of a

Answer 1

X=-1
ax^3+x^2+4a=9
-a+1+4a=9
3a=8
a=8/3

Answer 2

put x = -1 in the polynomial
$a( { - 1)}^{3} + ( { - 1)}^{2} + 4a - 9 = 0 \\ - a + 1 + 4a - 9 = 0 \\ 3a - 8 = 0 \\ 3a = 8 \\ a = \frac{8}{3}$