What is the 4th term of (3x+y)^7(3x+y)7?

1 Answer
bp
Apr 29, 2015

Consider the binomial expansion of (a+b)^n(a+b)n. (r+1)th term in this expansion is written as T_(r+1)= nC_r a^(n-r) b^rTr+1=nCran−rbr.

Now comparing the given expression, it can be seen that n=7, a= 3x, b= y and r=3(for getting the 4th term)

Accordingly, T_4= 7C_3 (3x)^4 y^3= 35*81 x^4y^3=2835x^4y^3T4=7C3(3x)4y3=35⋅81x4y3=2835x4y3

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