Solution
= Solution
The positive integrand factors into three one-variable functions on a rectangular domain. <Fubini's theorem> therefore gives
$$
\boxed{\left(\int_1^2x^{-2}dx\right)\left(\int_1^2y^{-3}dy\right)\left(\int_1^2z^{-4}dz\right)=\frac12\frac38\frac7{24}=\frac7{128}.}
$$