JEE Main2013MathematicsBinomial TheoremActual

If the 7th term in the binomial expansion of ( 3 [3] 84 + 3 x )^9, x>0 , is equal to 729 , then x can be:

Options

Ae^2
Be
Ce 2
D2 e

Correct answer

B. e

Step-by-step solution

Let r+1=7 r=6 Given expansion is ( 3 [3] 84 + 3 x )^9, x>0 We have T _ r+1 = ^n C _r(x)^ n-r a^r for (x+a)^n . According to the question aligned & 729= ^9 C ₆ ( 3 [3] 84 )^3 ( 3 x)^6 & 3^6=84 3^3 84 3^3 (6 x) & ( x)^6=1 ( x)^6=( e)^6 & x= e aligned

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