Bonjour;
12x+(-18x-5)
=12x -18x -5
= -6x-5
(2a-8a² + 3y) + (-3y+ 5a + 6a²)
= 2a-8a² + 3y -3y+ 5a + 6a²
= -2a² +7a
10a +5 (14a + 6b)
=10a +70a +30b
= 80a+30b
5a² - (6a+ 6a²)
= 5a² -6a -6a²
= -a² -6a
-3x² + (-2x²+7x-3) - (-5x² + 21x-3)
= -3x² -2x²+7x-3 +5x² - 21x+3
= -14x +3