∫ f'(lnx)/x dx = sinx + C
f'(lnx)/x = cosx
f'(lnx) = xcosx
f'(x) = e^x * cos(e^x)
f(x) = ∫ e^x * cos(e^x) dx = ∫ cos(e^x) d(e^x)
f(x) = sin(e^x) + C