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Question

Question: \(\int _ { 1 } ^ { 2 } \frac { \cos ( \log x ) } { x } d x =\)...

12cos(logx)xdx=\int _ { 1 } ^ { 2 } \frac { \cos ( \log x ) } { x } d x =

A

sin(log3)\sin ( \log 3 )

B

sin(log2)\sin ( \log 2 )

C

cos(log3)\cos ( \log 3 )

D

None of these

Answer

sin(log2)\sin ( \log 2 )

Explanation

Solution

Put t=logxdt=1xdxt = \log x \Rightarrow d t = \frac { 1 } { x } d x.

As x=2t=log2x = 2 \Rightarrow t = \log 2and x=1t=0x = 1 \Rightarrow t = 0, we have

=sin(log2)= \sin ( \log 2 ).