Answer:
31
Step-by-step explanation:
Given
x² + 5x - 3 = 0
with a = 1, b = 5, c= - 3 , then
sum of roots x₁ + x₂ = - = -
= - 5
product of roots = =
= - 3
Now
(x₁ + x₂)² = x₁² + 2x₁x₂ + x₂² , that is
(- 5)² = x₁² + 2(- 3) + x₂²
25 = x₁² - 6 + x₂² ( add 6 to both sides ), then
x₁² + x₂² = 31
Explanation:
Basically, you can do it in many ways. But just, in my opinion, exactly linear algebra was made for such cases.
the optimal way is to do it with Cramer's rule.
First, find the determinant and then find the determinant x, y, v, u.
Afterward, simply divide the determinant of variables by the usual determinant.
eg. and etc.
I think that is the best way to solve it without a hustle of myriad of calculations reducing it to row echelon form and solving with Gaussian elimination.