1.

Find the middle term in the expansion of (x/3 + 9y)10

Answer»

x = x/3, a = 9y, n = 10, r = 5 

n = 10 (even) there is only one middle term is (n/2 + 1) = (10/2 + 1) = 6th term 

General term Tr+1 = nCr xn-r ar ⇒ Ts+1 = 10C5 (x/3)10 - 5(9y)5 

T6 = 10C5 (x/3)5 g5 y5 ⇒ T6 = 10C5 . x5/35 × 95 y5 = 10C5 (xy)5 × (310/35)

T6 = [10C5 (xy)5 35] is the middle term.



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