+826 Find all $z$ such that neither $2+z-5z$ nor $2-z+8z$ is in the interval $(-7,13]$. Express your answer as an interval or as a union of intervals.
+129847 2 -4z < -7 2 -4z > 13
9 < 4z -11 > 4z
z > 9/4 z < -11/4
So....for the first one
(-inf, -11/4) U ( 9/4, inf)
2 + 7z < -7 2 + 7z > 13
7z < -9 7z > 11
z < -9/2 z > 11/7
So.... for the second one
(inf, -9/2) U (11/7, inf)
The most restrictive intervals are
(inf, -9/2) U ( 9/4 ,inf )
