Math miscellaneousMedium

Question

Coefficient of x9 in the expansion of is -

Options

A.0
B.7
C.14
D.21

Solution



⇒ cofficient of x22 in (x2 + 1)5(x4+1)4
⇒ 5Cr.x2r.4Crx4k
r = 3 & k = 4      r = 5 & k = 3
5C3.4C4     5C5.4C3
⇒10 + 4 = 14

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