x1²+x2²= (x1+x2)² - 2x1*x2
x1+x2 = -b/а = 13/5
(x1+x2)² = 169/25
x1*x2 = c/а = 4/5
2*x1*x2 = 2*c/а = 8/5
x1²+x2² = 169/25 - 8/5 = 169/25 - 40/25 = 129/25 = 5,16
x1²+x2²= (x1+x2)² - 2x1*x2
x1+x2 = -b/а = 13/5
(x1+x2)² = 169/25
x1*x2 = c/а = 4/5
2*x1*x2 = 2*c/а = 8/5
x1²+x2² = 169/25 - 8/5 = 169/25 - 40/25 = 129/25 = 5,16