Question
Question: If the 21<sup>st</sup> and 22<sup>nd</sup> terms in the expansion of (1 –x)<sup>44</sup> are equal, ...
If the 21st and 22nd terms in the expansion of (1 –x)44 are equal, then x =
A
7/8
B
–8/7
C
–7/8
D
None
Answer
–7/8
Explanation
Solution
T21 = T22
Ž T20+1 = T21+1
Ž 44C20 x20 = 44C21 (–x)21
Ž x =44C21−44C20= (20)!(24)!(44)!× (44)!(21)!(23)!
= 24−21= 8−7