Решить по формуле Виета.
x2−20x+51=0

x1+x2 x1⋅x2 x1 x2

x2-9x-52=0
x1+x2 x1⋅x2 x1 x2

А 20 без минуса?

без)

x² - 20x + 51 = 0x1 + x2 = -b/a = 20/1 = 20x1 * x2 = c/a = 51/1 = 51x1 = 17x2 = 3x² - 9x - 52 = 0x1 + x2 = -b/a = 9/1 = 9x1 * x2 = -52/1 = -52x1 = 13x2 = -4