Q.

The ratio of the coefficient of x10 in (1x2)10 and the term independent of 'x' in x2x10 is

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a

25:1

b

1:25

c

1:32

d

32:1

answer is D.

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Detailed Solution

Given, expansion is (1x2)10

Tr+1=nCr(1)nr(x2)r=10Cr(1)10r(x)2r(1)2r

for the x10 let 2r=10r=5

 6th term T6=T5+1=10C5(1)105(x)2(5)(1)2(5)

Coefficient of x10=10C5

Given, expression is x2x10

Tr+1=10Cr(x)10r2xr

=10Cr(x)10r(2)5(x)r=10Cr(x)102r(2)5

for independent of 'x' i.e., index of x=0

102r=02r=10

Question Image

6th term

T6=T5+1=10C5(x)102(5)(2)5

=(2)510C5

The ratio is  10C5:(2)510C5=+10C5+(2)510C5

=1:25=1:32.

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