(2x+1)(x-3) -(x-3)(7x+6)
2x²-6x+x-3 -(7x²+6x-21x-18)
2x²-5x-3 -7x²+15x+18
-5x² +10x+15
factorise
(2x+1)(x-3)-(x-3)(7x+6)
(x-3)(2x+1-7x-6)
(x-3)(-5x-5)
-5(x-3)(x+1)
3/
pour x = 2
-5x² +10x+15
-5(2)² +10(2) +15
-5(4) + 20+15
-20+20+15
15
pour x = -3
-5x² +10x+15
-5(-3)² +10(-3) +15
-5(9) -30+15
-45 -30 +15
-60
pour x = 1/2
-5x² +10x+15
-5(1/2)² +10(1/2) +15
-5(1/4) +5 +15
-5/4 +20
-5/4 +80/4
75/4
pour x = V3
-5x² +10x+15
-5(V3)² +10V3+15
-5(3) +10V3+15
-15+10V3+15
+10V3
4/ resoudre a = 0
-5(x-3)(x+1) = 0
x-3 = 0 x+1 = 0
x = 3 x = -1
solution (-1; 3)