Question

What is the coefficient of the term x^7y in the expression of (x+y)^8?

Answer 1

(r + 1)th term of (a + b)^n = nCr a^(n-r)b^r

here n = 8 , r = 8-7 = 1, a = a and b = y

so we need second term where r = 1:-
= 8 C 1 x^7y

so the coefficient is 8