Multiply both sides by z + 1: 3 - z >= z + 1
Then 2z <= 2, so z <= 1.
Solution: (-inf,1].
You're very new to math, in this case, if you include -1 in the denominator, the answer is undefined, so you're WRONG. The answer is (−∞,−1)U(−1,1)
You're very new to math too, as if the answer is negative and lower than -1 then it will be less than 1. so the answer then, is obviously (-1, 1]
Ignoring the toxic "discussion" above and actually solving the problem:
3−zz+1≥13−zz+1(z+1)2≥(z+1)2 and z+1≠0(3−z)(z+1)≥(z+1)2 and z+1≠0−z2+2z+3≥z2+2z+1 and z+1≠02z2−2≤0 and z+1≠0z2−1≤0 and z+1≠0−1≤z≤1 and z≠−1−1<z≤1