I have no idea how

Quote:

-4(4-x)^2<8-(4-2x)^2

(4-x) ² = 16 - 8x + x ²

(4-2x) ² = 16 - 16x + 4x ²

substituting these in

-4 (16 - 8x + x ²) < 8 - (16 - 16x + 4x ²)

multiply everything out

-64 + 32x - 4x ² < 8 - 16 + 16x - 4x ² = -8 + 16x - 4x ²

combine all the like terms

-56 + 16x < 0

16x < 56

x < 56/16 = 7/2