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Joint Entrance Examination
Mathematics
Binomial Theorem
Question 308
Question 308 of 347
Medium
MCQ
The coefficient of x18 in the product (1 + x) (1 -- x)10 (1 + x + x2)9 is :
A
126
B
- 84
C
- 126
D
84
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Official solution
Coefficient of x18 in (1 + x) (1 - x)10 (1 + x + x2)9 \[ \Rightarrow \] Coefficient of x18 in {(1 - x) (1 - x2) (1 + x + x2)}9 \[ \Rightarrow \] Coefficient of x18 in (1 - x2) (1 - x3)9 \[ \Rightarrow \] 9C6 - 0 = 84
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