Question
Question: The coefficient of x<sup>5</sup> in the expansion of (1 + x<sup>2</sup>)<sup>5</sup> (1 + x)<sup>4</...
The coefficient of x5 in the expansion of (1 + x2)5 (1 + x)4 is –
A
30
B
60
C
40
D
None of these
Answer
60
Explanation
Solution
(5C0 + 5C1 x2 + 5C2 x4 + 5C3 x6 + ...... ) ×
(1 + 4C1x + 4C2 x2 + 4C3 x3 + 4C4 x4)
Now, coefficient of x5
= 5C1 × 4C3 + 5C2 × 4C1
= 20 + 40 = 60