Bonjour,
K=x-6 - 5x²- 30-x=
-5x² -36
L=12x - x²- 10 + x - 3 - 8x² + 1-2x=
-9x² + 11x -16
M= -3 - a + b + 5a - 9 + (-3a - 5a)=
-3 - a + b + 5a - 9 -3a + 5a=
6a +b -12
N=x² - (3x² - 15 + 4) + (15x²- 12x - 3)=
x² - 3x² +15 - 4 +15x²- 12x - 3=
13x² -12x +8