9x²+3x-2=0
D = 9+4*9*2 = 81
x1 = (-3-9):9 = -12/9 = -4/3 = -1 1/3
x2 = (-3+9):9 = 6*9 = 2/3
5x²+10x = 0
5x(x+2) = 0
x1 = 0
x2 = -2
9x²-4 = 0
9x² = 4
x² = 4/9
x = ±2/3
x²-7x+6 = 0
D = 49-4*6 = 49*24 = 25
x1 = (7-5):2 = 2:2 = 1
x2 = (7+5):2 = 12:2 = 6
2x²+3x+4 = 0
D = 9-4*2*4 = 9-32 = -23<0 - корней нет.