binomial theorem-1-
2009-10-26 10:59 pm
Let Ar be the coefficients x^r in the expansion of {x^2 + [a / (2x)]} ^7, where a≠0. If A8 = 6A11, find the value of a.
回答 (1)
2009-10-27 2:17 am
✔ 最佳答案
For x8, it should be 7C5 (x2)5 [a/(2x)]2Coefficient = 21a2/4
For x11, it should be 7C6 (x2)6 [a/(2x)]
Coefficient = 7a/2
Thus,
21a2/4 = 7a/2
21a/4 = 7/2
a = 2/3
參考: Myself
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