Question

Find the value of b, if (x - 3) is a factor of $x^3-9x^2$ - bx + 81 = 0

• A. b = 4
• B. b = 7
• C. b = 9
• D. b = 8

Answer 1

The correct option is C

b = 9

(x - 3) is a factor of f(x) = $x^3-9x^2$ - bx + 81

$\Rightarrow$ f(3) = 0

$\Rightarrow$ $3^3-9(3{)}^2$ - 3b + 81 = 0

$\Rightarrow$ 27 - 3b = 0 $\Rightarrow$ b = 9