a bout the binomail theorem -__-?

Question

hi guyz

Can any one help me in this

Find b if the coefficint of x^11 in the expantion (x^2 +1/bx)^10 ????

Answer 1

Each term in the expansion has the form C(10,a)*[(x^2)^a]*[1/^(bx)]^(10-a) = C(10,a)*[x^(2a)]*{1/[b^(10-a) x^(10-a)]} = C(10,a)*[x^(2a-(10-a))]/[b^(10-a)]. Therefore, the exponent on x is 2a - (10 - a) = 3a - 10. That exponent is 11 when a = 7, so the coefficient is C(10,7) = 10!/[7! 3!] = 120.

Answer 2

What is coefficient of x^11????