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