NCERT Class XI Mathematics - Binomial Theorem - Solutions
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Question : 20
Total: 36
Find the 13th term in the expansion of ( 9 x −
) 18
Solution:
We know that the (r + 1)th term in the expansion of ( x + a ) n
t r + 1
C r x n − r a r
Then (r + 1)th term in the expansion of( 9 x −
) 18
T r + 1
C r ( 9 x ) 18 − r ( −
) r
For 13th term, we have r + 1 = 13 i.e., r = 12
∴T 13
C 12 ( 9 x ) 18 − 12 ( −
) 12 ( 9 x ) 6
Then (r + 1)th term in the expansion of
For 13th term, we have r + 1 = 13 i.e., r = 12
∴
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