Let say f(x) = $$x^3 + 2x^2 + bx + 68$$ and given (x+4) is a factor of f(x).
$$\Rightarrow f(x) = (x+4)\times k$$.................(1)
where 'k' is the quotient when f(x) is divided by (x+4).
Substituting 'x= -4' in the equation (1), we get
f(-4) = 0
$$\Rightarrow -4^3 + 2 (-4)^2 + b (-4) + 68 = 0$$
$$\Rightarrow -64 + 32 - 4b + 68 = 0$$
$$\Rightarrow 4b = 36$$
$$\Rightarrow b = 9$$.
Create a FREE account and get: