Bonsoir,
(7+2x)+(5+2x) = 7+2x+5+2x = 12+4x
(4+9x)-(2x+1) = 4+9x-2x-1 = 3+7x
(-9x-1)-(3x-8) = -9x-1-3x+8 = -12x+7
(x²+3)+(9x²+4) = x²+3+9x²+4 = 10x²+7
3x²+5-(7x²+9x-3) = 3x²+5-7x²-9x+3 = -4x²-9x+8
4x²-(3x²+9)+9 = 4x²-3x²-9+9 = x²
-x+(-5+2x) = -x-5+2x = x-5
-5x×2x-(-9x²-9) = -10x²+9x²+9 = -x²+9
