-2x^2-8x-4=y,
-2(x^2+4x+2)=y,
x^2+4x+2=-½y,
(x^2+4x+4)-2=-½y,
(x+2)^2=2-½y,
x+2=√(2-½y),
x=√(2-½y) - 2,
2-½y≥0,
-½y≥-2,
y≤4,
Ey=(-∞;4]
-2x^2-8x-4=y,
-2(x^2+4x+2)=y,
x^2+4x+2=-½y,
(x^2+4x+4)-2=-½y,
(x+2)^2=2-½y,
x+2=√(2-½y),
x=√(2-½y) - 2,
2-½y≥0,
-½y≥-2,
y≤4,
Ey=(-∞;4]