If the coefficients of   terms of are in arithmetic progression, then find the value of r:

Asked by Topperlearning User | 4th Jun, 2014, 01:23: PM

Expert Answer:

 
Since the terms of given expansion are in arithmetic progression, we have,
           
or (15-2r) (r +1) = (13-2r) (15 –r)
or 15r + 15 - - 2r = 195 – 30r -13r +
or - 56r + 180 = 0
or - 4r + 45 = 0
or (r - 5) (r- 9) = 0
r = 5, 9.

Answered by  | 4th Jun, 2014, 03:23: PM