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Question
If x + 1 is a factor of 3x3 + kx2 + 7x + 4, then the value of k is
Options
– 1
0
6
10
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Solution
f(x) = 3x3 + kx2 + 7x + 4
g(x) = x + 1
Remainder = 0
Let x + 1 = 0,
then x = – 1
f(– 1) = 3(– 1)3 + k(– 1)2 + 7(– 1) + 4
= – 3 + k – 7 + 4
= k – 6
∴ Remainder = 0
∴ k – 6 = 0
⇒ k = 6.
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