Question
The integral $$\int\limits_2^4 {\frac{{\log \,{x^2}}}{{\log \,{x^2} + \log \,\left( {36 - 12x + {x^2}} \right)}}} dx,$$ is equal to:
A.
$$1$$
B.
$$6$$
C.
$$2$$
D.
$$4$$
Answer :
$$1$$
Solution :
$$\eqalign{
& I = \int\limits_2^4 {\frac{{\log \,{x^2}}}{{\log \,{x^2} + \log \,\left( {36 - 12x + {x^2}} \right)}}} \cr
& I = \int\limits_2^4 {\frac{{\log \,{x^2}}}{{\log \,{x^2} + \log \,{{\left( {6 - x} \right)}^2}}}} .....(1) \cr
& I = \int\limits_2^4 {\frac{{\log \,{{\left( {6 - x} \right)}^2}}}{{\log {{\left( {6 - x} \right)}^2} + \log \,{x^2}}}} .....(2) \cr
& {\text{Adding (1) and (2), we get}} \cr
& 2I = \int\limits_2^4 {dx} = \left[ x \right]_2^4 = 2\,\,\, \Rightarrow I = 1 \cr} $$