Say I have the integral
$$ \int_0^{10} 1\ d(x^2) $$
Are the limits on the range of $x$ or of $x^2$ ?
Based on the wiki page I am assuming it is the limits of $x$ in which case I imagine the answer here is:
$$ \int_0^{10} 1\ d(x^2) = \int_0^{10} 2x\ dx = [x^2]^{10}_0 = 100 $$
Or alternatively is it a limit on $x^2$ ? e.g. using $z = x^2$
$$ \int_0^{10} 1\ d(x^2) = \int_0^{10} 1\ dz = [z]^{10}_0 = 10 $$
Any help / clarification would be appreciated !