Bjr,
1)
5x² + 10x = 0
5x * 5x + 5x * 2 = 0
5x(2 + x) = 0
5x = 0
x = 0/5 = 0
et
2 + x = 0
x = 0 - 2 = -2
2)
x² - 81 = 0
(-9 + x)(9 + x) = 0
- 9 + x = 0
x = 0 + 9 = 9
et
9 + x = 0
x = 0 - 9 = - 9
3)
(x - 3)² - 49 = 0
x² - 6x + 9 - 49 = 0
x² - 6x - 40 = 0
(4 + x)(-10 + x) = 0
4 + x = 0
x = - 4
et
- 10 + x = 0
x = 0 + 10 = 10