2x² - 7x - 30 = 0
D = b² - 4ac
a = 2
b = -7
c = -30
D = (-7)² - 4 * 2 * (-30) = 49 + 240 = 289 (√289 = 17)
x1 = (7 + 17)/2 = 24/2 = 12
x2 = (7 - 17)/2 = -10/2 = -5
D = 169 it is determinant
x1 = 5
x2 = -1.5
