
Michael F. answered 04/03/14
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Mathematics Tutor
(-2x6+(5/x))21=(-2x7+5)21/x21
The coefficient of x21 in the expansion of the numerator is what we want
(-2x7+5)21=∑k=0k=21(21Ck)(-2x7)k521-k
The term of interest is that for k=3 or 21C3(-8)518=(-8)(21×20×19/(1×2×3))×518
Excel gives me -40588378906250000 or -4.058837890625E+16
Michael F.
(-2x6)3=-8x18
04/03/14