Question

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

Answer 1

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

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^3`