what is the coefficient of the xpower 3 in 7
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Explanation:
for integers the binomial expansion is
(x+y)n=xn+nC1xn−1y+nC2nn−2y2+....nCkxn−kyk+.....yn
where nCk=n!k!(n−k)!
for (x−3)7
the term including x5
7C2x5(−3)2
=7!2!(5!)×9
=(7×6×5!2×5!)×9
=21×9=189
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