[tex]a)\quad E(x) = (x+5)^2+2(x+5)(x-2)+(x-2)^2\\ \\ =\left[(x+5)+(x-2)\right]^2 = (2x+3)^2\\ \\\\ b)\quad E(t) = \underset{\geq 0}{\underbrace{(2t+3)^2}}\Rightarrow \boxed{t\in \{-2,-1\}}[/tex]
[tex]\text{Pentru }t = -2:\quad E(-2) = (-4+3)^2 = 1\\\text{Pentru }t = -1:\quad E(-1) = (-2+3)^2 = 1[/tex]