F(x)=-5x
g(x)=8x^2-5x-9
find (f•g)(x)
a.-40x^4+25x^3+45x^2
b.-40x^3-5x-9
c.-40x^2+25x+45x
d.-40x^3+25^2+45x

D. -40x^3 + 25x^2 + 45x

Step-by-step explanation:

-5x(8x^2 - 5x - 9)

-40x^3 + 25x^2 + 45x

the answer is b

let's call the solutions x₁ = (5 - 2√7)/3 and x₂ = (5 + 2√7)/3

then the equation is (x-x₁)(x-x₂) = 0

if you fill that in you get a lot of numbers which you can recognize as ax²+bx+c=0.

step-by-step explanation:

you can see that a=1 (there is just an x²)

b = (-5 -2√7 + 2√7 - 5)/3 = -10/3

c = -2√7)/3 ) * (-5+2√7)/3) = -1/3

so your answer is 3x^2 – 10x – 1 = 0