Why is (a/b) ² +(b/a) ² = (a/b + b/a) ² - 2?

Answer 1

x² + y² = (x + y)² - 2xy

Then

(a/b)² + (b/a)² = ((a/b) + (b/a))² - 2(a/b)(b/a)

See the last step?

Answer 2

Answer 3

a/b=b/a=1 so 1^2+1^2=2

(1+1)^2-2=2