InterviewSolution
Saved Bookmarks
| 1. |
The coefficients of three consecutive terms of `(1+x)^(n+5)`are in the ratio 5:10:14. Then `n=`___________.A. 5B. 7C. 6D. 8 |
|
Answer» Correct Answer - c Let `t^(th), (r +1)^(th) and (r +2)^(th)` be three consecutive terms in the expansion of `(1 + x)^(n+5)`. It is given that `""^(n+5)C_(r-1) :""^(n+5)C_(r) :""^(n+5)C_(r+1) = 5:10:14` `rArr (""^(n+5)C_(r))/ (""^(n+5)C_(r-1)) =(10)/(5) and (""^(n+5)C_(r+1))/(""^(n+5)C_(r)) =(14)/(10)` `rArr (n+5 - r +1)/(r) = 2 and ((n+5) -r)/(r+1) = (7)/(5)` `rArr n- 3r + 6 = 0 and 5n - 12r + 18 = 0` `rArr n = 6 , r = 4` |
|