Let $F(x)=f(x)+f\left(\frac{1}{x}\right)$, where $f(x)=\int_1^x \frac{\log t}{1+t} d t$. Then $F(e)$ equals
Let $F(x)=f(x)+f\left(\frac{1}{x}\right)$, where $f(x)=\int_1^x \frac{\log t}{1+t} d t$. Then $F(e)$ equals
-
$\frac{1}{2}$
-
$0$
-
$1$
-
$2$
Solution
$f(x)=\int_1^x \frac{\log t}{1+t} d t$
$F(e)=f(e)+f\left(\frac{1}{e}\right)$
$F(e)=\int_1^e \frac{\log t}{1+t} d t+\int_1^{1 / e} \frac{\log t}{1+t} d t$
$=\int_1^e \frac{\log t}{1+t}+\int_1^e \frac{\log t}{t(1+t)} d t$
$=\int_1^e \frac{\log t}{t} d t=\frac{1}{2}$.
Asked in: JEE Main 2007
Practice more Definite Integration questions on Aicharya