Question
Question: If the coefficients of 2<sup>nd</sup>, 3<sup>rd</sup> and 4<sup>th</sup> terms in the expansion of (...
If the coefficients of 2nd, 3rd and 4th terms in the expansion of (1 + x)2n are in A.P., then 2n2 – 9n + 8 =
A
0
B
1
C
– 1
D
None
Answer
1
Explanation
Solution
We know that is rth (r + 1)th (r + 2)th term coefficient are in an A.P. then m2 – (4r + 1) m + 4r2 – 2 = 0 then for 2nd 3rd , 4th term r = 2, m = 2n
(2n)2 – 9 × 2n + 14 = 0
2n2 – 9n + 7 = 0
2n2 – 9n + 8 = 1