Coefficient of x9 in the expansion of is -

⇒ cofficient of x22 in (x2 + 1)5(x4+1)4⇒ 5Cr.x2r.4Crx4kr = 3 & k = 4 r = 5 & k = 35C3.4C4 5C5.4C3⇒10 + 4 = 14

Math miscellaneousHard

Question

Coefficient of x⁹ in the expansion of is -

A.0

B.7

C.14

D.21

⇒ cofficient of x²² in (x² + 1)⁵(x⁴+1)⁴
⇒ ⁵C_r.x^2r.⁴C_rx^4k
r = 3 & k = 4 r = 5 & k = 3
⁵C₃.⁴C₄ ⁵C₅.⁴C₃
⇒10 + 4 = 14

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