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Question

If the coefficient of x in the expansion of (x2+kx)5 is 270, then k =


A

1

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B

2

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C

3

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D

4

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Solution

The correct option is C

3


Tr+1 = 5Cr(x2)5r(kx)r

For coefficient of x, 10 - 2r - r = 1 ⇒ r = 3

Hence, T3+1 = 5C3(x2)53(kx)3

According to question, 10k3 = 270 ⇒ k = 3.


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