2^(x²) <= 4•2^x
2^(x²) <= 2^(x+2)
x² <= x+2
x²-x-2 <= 0
x²-2x+x-2 <= 0
x(x-2)+x-2 <= 0
(x-2)(x+1) <= 0
+. -. +
[-1][2]
x€[-1; 2]
