Question #19f75

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Answer 1 · 2016-09-18T20:03:20

$a = \frac{1}{3}, and, n = 6$ $a=1/3, and, n=6$ .

Knowing that,

$(1+ax)^n=1+n*ax+n*(n-1)/2*a^2x^2+...+a^nx^n$ , we have,

$an=2... ... ...(1), and, n*(n-1)/2*a^2=5/3... ... ...(2)$

$"From "(2), (na)((n-1)/2*a)=5/3, i.e., (na)((na-a))/2=5/3$ .

$"Then "(1) rArr (2)((2-a))/2=5/3, or, (2/2-a/2)=5/6$

$:.-a/2=5/6-1=-1/6$

$:. a=1/3$ .

$"By "(1)", then, "1/3*n=2 rArr n=6$ .

Enjoy maths.!