Question

If f'(x)=2/x and f(sqrt(e))=5, then f(e)=

Answer 1

$f'(x)=\dfrac2x$
$\implies f(x)=\displaystyle\frac2x\,\mathrm dx=2\ln|x|+C$

$f(\sqrt e)=5\implies 5=2\ln|\sqrt e|+C$
$\implies 5=\dfrac22\ln e+C$
$\implies C=4$
$\implies f(x)=2\ln|x|+4$
$\implies f(e)=2\ln|e|+4=6$