Mathematics
JAMB 2006
Find the value of k if the expression kx
3 + x
2 - 5x - 2 leaves a remainder 2 when it is divided by 2x + 1
Correct Answer: Option C
Explanation
F(x) = Q x D + R
Kx
3 + x
2 - 5x – 2 = Q(2x+1)+R
If 2x+1 = 0 implies x = -
1/
2
∴k(-
1/
2)
3 + (-
1/
2)
2 -5(-
1/
2) -2
= Q(2(-
1/
2) + 1) +2
K(-
1/
8) +
1/
4 +
5/
2 - 2 = Q(-1+1)+2
-
k/
8 +
1/
4 +
5/
2 - 2 = 0+2
(-k+2+20-16) / 8 = 2
(-k+6) / 8 = 2
-k+6 = 2*8
-k+6 = 16
-k = 16-6
-k = 10
∴k = -10
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