2(x-4(x+5)x-4(2x-x^2)=0

х - 4х -20 - 8х +4х² = 0
4х²-11х -20 = 0
D = 441
х₁ = (11 +21)/8 = 32/8 = 4
х₂ = (11 - 21)/8 = -10/8 = -5/4 = -1,25