NTA Abhyas JEE Main2020MathematicsBinomial TheoremPractice
In the binomial expansion of 2 3 + 1 3 3 n , the ratio of the 7 t h term from the beginning to the 7 t h term from the end is 1 : 6 , then the value of n is
Options
- A13
- B16
- C9
- D23
Correct answer
C. 9
Step-by-step solution
7 t h term from the beginning is C 6 n 2 n - 6 3 1 3 6 3 7 t h term from the end is C 6 n 1 3 n - 6 3 2 6 3 ⇒ n C 6 2 n 3 - 2 1 3 2 n C 6 2 2 1 3 n 3 - 2 = 1 6 ⇒ 2 n 3 - 4 1 3 4 - n 3 = 1 6 ⇒ 2 × 3 n 3 - 4 = 2 × 3 - 1 ⇒ n = 9