Question #19f75

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Answer 1 · 2016-09-18T20:03:20

#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.!