Q. 24.1( 36 Votes )

# Find a if the coefficients of x^{2} and x^{3} in the expansion of (3 + ax)^{9} are equal.

Answer :

We know that-

General term of expansion (a+b)^{n} is

For (3+ax)^{9}

Putting a = 3, b = ax & n = 9

General term of (3+ax)^{9} is

Since we need to find the coefficients of x^{2} and x^{3}, therefore

For r = 2

Thus, the coefficient of x^{2} =

For r = 3

Thus, the coefficient of x^{3} =

Given that-

Coefficient of x^{2} = Coefficient of x^{3}

∴ a = 9/7

Hence, a = 9/7

Rate this question :

Show that the coefficient of x^{4} in the expansion of is .

Show that the middle term in the expansion of is 252.

RS Aggarwal - MathematicsShow that the coefficient of x^{-3} in the expansion of is -330.

Show that the term independent of x in the expansion of is -252.

RS Aggarwal - MathematicsFind the middle term in the expansion of

RS Aggarwal - MathematicsIf the 17^{th} and 18^{th} terms in the expansion of (2 + a)^{50} are equal, find the value of a.