Question

If xy=15 and x+y=5, find x^2+y^2

Answer 1

- 5

Explanation:

Note that

(x + y)² = x² + 2xy + y², thus

x² + y² = (x + y)² - 2xy ← substitute given values

= 5² - 2(15)

= 25 - 30

= - 5