NTA Abhyas JEE Main2020MathematicsBinomial TheoremPractice
The coefficient of x 10 in the expansion of 1 + x 15 + 1 + x 16 + 1 + x 17 + . . . + 1 + x 30 is
Options
- A31 C 10 - 15 C 10
- B31 C 11 - 15 C 11
- C30 C 10 - 15 C 10
- D31 C 10 - 14 C 11
Correct answer
B. 31 C 11 - 15 C 11
Step-by-step solution
Coefficient of x 10 in the given expansion = 15 C 10 + 16 C 10 + 17 C 10 + . . . 30 C 10 = 10 C 10 + 11 C 10 + . . . + 14 C 10 + 15 C 10 + . . . + 30 C 10 - 10 C 10 + 11 C 10 + . . . + 14 C 10 = 31 C 11 - 15 C 11