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Question

In the expansion of ((5)12+(7)18)1024, the number of integral terms is


Your Answer
A
128
Correct Answer
B
129
Your Answer
C
130
Your Answer
D
131

Solution

The correct option is B 129
Tr+1=1024Cr(5)121024r(7)18rTr+1=1024Cr(5)(1024r)/2(7)r/8
Now, this term will be an integer if
1024r2,r8 will be an integer, for which r has to be multiple of 8.
r=0,8,16,,1024
For A.P. 0,8,16,,1024,
number of terms will be 10248+1=129

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