Problems

Suppose that: $$\frac{x+y}{x-y}+\frac{x-y}{x+y}=3.$$ Find the value of the following expression: $$\frac{x^2+y^2}{x^2-y^2}+\frac{x^2-y^2}{x^2+y^2}.$$

A broken calculator carries out only one operation “asterisk”: $a\ast b=1-a/b$. Prove that using this calculator it is possible to carry out all four arithmetic operations (addition, subtraction, multiplication, division).