Question

If coefficients of 2^nd, 3^rd and 4^th terms in the binomial expansion of $5^{n} - 4^{n}$ are in A.P., then $5^{n + 1} - 4^{n + 1}$ is equal to.

• A. – 7
• B. 7
• C. 14
• D. – 14

Answer 1

Answer: (D)

– 14

Answer 2

Coefficients of 2^nd, 3^rd and 4^th terms are

respectively $+ (T_{1} - T_{3} + T_{5} - ....)^{2} =$ and $(x^{2} + a^{2})$ are in A.P.

⇒ $(x^{2} + a^{2})^{n}$

⇒ $(x^{2} + a^{2})^{1/n}$

On solving, $(x^{2} + a^{2})^{- 1/n}$.