Question

If the coefficients of x⁷ and x⁸ in (2 + x/3)ⁿ are equal, then n is

(a) 56 

(b) 55

(c) 45 

(d) 15

Answer 1

B is the correct choice.

Since T_{r + 1} = ⁿC_r a^{n – r} x^r in expansion of (a + x)ⁿ,

Therefore,

and

Therefore,

(since it is given that coefficient of x⁷ = coefficient x⁸)