JAMB - Mathematics (1992 - No. 14)
If x + 1 is a factor of x3 + 3x2 + kx + 4, find the value of k
6
-6
8
-8
Explicació
x + 1 is a factor of x3 + 3x2 + kx + 4
Let f(x) = x3 + 3x2 + kx + 4
∴ f(-1) = (-1)3 + 3(-1)2 + k(-1) + 4 = 0
-1 + 3 - k + 4 = 0
∴ k = 6
Let f(x) = x3 + 3x2 + kx + 4
∴ f(-1) = (-1)3 + 3(-1)2 + k(-1) + 4 = 0
-1 + 3 - k + 4 = 0
∴ k = 6