Bonsoir,
5)
3x² = 8
x² = 8/3
x1 = [tex]+\sqrt{8/3}[/tex] et X2=[tex]-\sqrt{8/3}[/tex]
6)
2 x ² + 3 = 0
2 x ² = -3
x ² = -3/2
pas de solution une racine carré doit être positive
7)
3 x ² - 14 = 0
3 x ² = 14
x ² = 14/3
X1 = +[tex]\sqrt{14/3}[/tex] ou X2 = -[tex]\sqrt{14/3}[/tex]
8)
x (x – 2) = x ² + 16
x ² - 2x = x ²+ 16
-2x = 16
x=-16/2
x=-8
9)
-6 x ²+ 5 = 4 x ² - 3
-6 x ²- 4 x ² = - 3 - 5
-10 x ²= - 8
10 x ²= 8
x ²= 8 / 10
x ²= 4 / 5
x1 = +[tex]\sqrt{4/5}[/tex] ou x2 = x1 = -[tex]\sqrt{4/5}[/tex]
tu peux simplifier : [tex]\sqrt{4/5}[/tex] = [tex]2\frac{\sqrt{2} }{5}[/tex]
10)
(x + 2)² = (x + 3)(x - 5)
(x + 2)² = x² - 2x - 15
x² + 4 + 4x = x² - 2x - 15
4 + 4x = - 2x - 15
4x + 2x = - 15 -4
6x = -19
x=-19/6
11)
(x - 1)(x + 1) = (x + 2)(x + 3)
x² - 1 = x² + 5x + 6
- 1 = + 5x + 6
- 7 = + 5x
x=-7/5
12)
8x²- 7x + 11 = -4x ² - 5 + (12x – 3)(x + 2)
8x²- 7x + 11 = 8x ² - 11 + 21x
- 7x + 11 = - 11 + 21x
- 7x - 21x = - 11 -11
- 28x = - 22
x = 2*11/2*14
x=11/14
