Question

(x+y)^2-(x-y)^2 = 20

Answer 1

(x + y)² - (x - y)² = 20

x² + 2xy + y² - (x² - 2xy + y²) = 20

x² + 2xy + y² - x² + 2xy - y² = 20

4xy = 20 --> xy = 20/4 ---> xy = 5