X+y=9 xy=-10 система квадратных уравнений

x + y = 9 xy = - 10 x = 9 - y y (9 - y ) + 10 = 0 * 9y - y^2 + 10 = 0  - y^2 + 9y +10 = 0  y^2 - 9y - 10 = 0  D = 81 + 40 = 121 = 11^2 y1 = ( 9 + 11)/2 = 20/2 = 10; y2 = ( 9 - 11)/2 = - 2/2 = - 1; y1 = 10 x1 = 9 - y1 = 9 - 10 = - 1; y2 = - 1 x1 = 9 - y2 = 9 + 1 = 10  Ответ ( - 1; 10) ( 10; - 1)