Question 668500
Using the binomial theorem for (a+b) kth term of exponent n, we get (n choose k) * a^(n-k) * b^k 
(6 choose 5)*{{{a^(6-5) * (-b)^(5) = 6*a^1(-b)^5 = 6a(-b)^5 = -6ab^5}}}