Dealing with absolute value norm in multiple integral type questions

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I have a common question concerning the three integral questions below.
I don't know how to deal with terms like $|x|$. I can parameterize both the region of integration or the integrand, but do I have to consider the two cases for $x < 0$ or $x \geq 0$

One other thing, isn't the region $|x|+|y|+|z| \leq 1$ suppose to be called an octahedron. So when i integrate over this region, should it not be two times the integral over a tetrahedron.

Thank you in advance.

Integrate the function $f(x,y,z)={x}^{2}+{y}^{2}+{z}^{2}$ over the tetrahedron

$\ E=\{(x,y,z): |x|+|y|+|z| \leq 1\} $

Integrate the function $f(x,y,z)=|z|$ over the tetrahedron

$\ E=\{(x,y,z): |x|+|y|+|z| \leq 1\} $

Integrate $f(x,y,z)=|z|$ over the surface of the sphere

$\ E=\{(x,y,z):{x}^{2}+{y}^{2}+{z}^{2}=1\} $