Bonjour,
(a+b)² = a²+2ab+b²
(a-b)² = a²-2ab+b²
donc :
(x-4)²+(x+2)² = (x²-8x+16)+(x²+4x+4) = 2x²-4x+20
(x+5)²-(2x-4)² = (x²+10x+25)-(4x²-16x+16) = -3x²+26x+9
48-3(2x+1)² = 48-3(4x²+4x+1) = 48-12x²-12x-3 = -12x²-12x+45
3x+2(2x-1)² = 3x+2(4x²-4x+1) = 3x+8x²-8x+2 = 8x²-5x+2