1. 7х² - 9х + 2 = 0
Д = 9² - 4 × 2 × 7 = 81 - 56 = 25
корень из 25 = 5
х1 = 9 + 5/2 × 7 = 14/14 = 1
х2 = 9 - 5/2 × 7 = 4/14
2. 5х² = 12х
5х² - 12х = 0
х(5х - 12) = 0
х1 = 0
х2 = 12/5 = 2.4
3. 7х² - 28 = 0
7х² = 28
х² = 4
х1 = 2
х2 = -2
4. х² + 20х + 91 = 0
Д = 20² - 4 × 91 = 400 - 364 = 36
корень из 36 = 6
х1 = -20 + 6/2 = -14/2 = -7
х2 = -20 - 6/2 = -26/2 = -13
1) x¹=2/7 x²=1
2) x¹=0 x²=12/5
3) x¹=-2 x²=2
4)(x+3)(x+17),=0
