I have to determine the coefficient of an x term in an expansion such as this; Determine the coefficient of x^18 in the expansion of (1/14 x^2 -7)^16 The general term in the binomial expansion is nCk a^k b^(n−k) I could let a = (1/14 x^2) b = -7 n = 16 k = 9? I have no real idea of how to go about finding this coefficient using the binomial theorem. Having expanded the expression to the 10th term I get 8C9 (-7) (1/14 x^2)^9 I'm using nCk = n! / (n-k)!k! but can't evaluate this as it is a negative. I'm assuming that the 8C9 bit is just the opposite of 6th term i.e. 12C5 = 792 (looking at Pascal's triangle this is on the opposite side), but I can get the x^18 bit (I'm assuming the (x^2)^9 can be x^18 here) Can someone check, please?