STD 12 - 7.2 definite integral — JEE STD 11 Science — Question

$\Rightarrow I'(b) = \int_0^1 {\frac{{{x^b}\log x}}{{\log x}}dx} $

(If $I(\alpha ) = \int_0^b {f(x,\alpha )dx} $, then $I'(\alpha ) = \int_0^b {f'(x,\alpha )dx} $, 

where $f'(x,\alpha )$ is derivative of $f(x,\alpha )$ w.r.t. $\alpha $ keeping $x$ constant)

$I'(b) = \int_0^1 {{x^b}dx = \frac{1}{{b + 1}}} $

==> $I(b) = \int {\frac{{db}}{{b + 1}} + c = \log (b + 1) + c} $

If $b = 0$, then $I(b) = 0$, 

so $c = 0$==>$I(b) = \log (b + 1)$.