Find the coefficient of x1/17 in the expansion of (x4 – 1/x3)15
Given: (x4 – 1/x3)15
Thus,
Tr+1 = 15Cr(x4)15-r(-1/x3)r
= 15Cr x60-4r(-1)r x-3r
= 15Cr x60-7r(-1)r
Now, for coefficient x-17,
60 – 7r = -17
7r = 77
r = 11
Thus, T11+1 = 15C11 x60-77(-1)11
Therefore,
Coefficient of x-17 = -15 x 14 x 13 x 12 x 11!/11! x 4 x 3 x 2 x 1
= -1365