CameraIcon
CameraIcon
SearchIcon
MyQuestionIcon
MyQuestionIcon
1
You visited us 1 times! Enjoying our articles? Unlock Full Access!
Question

If the 2nd, 3rd and 4th terms in the expansion of (x + a)n are 240, 720 and 1080 respectively, find x, a, n.

Open in App
Solution

In the expansion of x+an, the 2nd, 3rd and 4th terms are C1n xn-1 a1, C2n xn-2 a2 and C3n xn-3 a3, respectively.According to the question,C1n xn-1 a1=240 C2n xn-2 a2=720C3n xn-3 a3=1080C2n xn-2 a2C1n xn-1 a1=720240n-12xa=3ax=6n-1 ...1Also,C3n xn-3 a3C2n xn-2 a2=1080720n-23xa=32ax=92n-4 ...2Using 1 and 2 we get6n-1=92n-4n=5Putting in eqn1 we get2a=3xNow, C15 x5-1 32x=24015x5=480x5=32x=2By putting the value of x and n in 1 we geta=3

flag
Suggest Corrections
thumbs-up
1
Join BYJU'S Learning Program
similar_icon
Related Videos
thumbnail
lock
General Term
MATHEMATICS
Watch in App
Join BYJU'S Learning Program
CrossIcon