Question

Помогите пожалуйста!

Answer 1

$(z-\frac{z}{y})(z+\frac{z}{y})=z^{2}-(\frac{z}{y})^{2} =z^{2}-\frac{z^{2}}{y^{2}}=\frac{z^{2}y^{2} -z^{2}}{y^{2}}=\frac{z^{2}(y^{2}-1)}{y^{2}}\\\\Otvet:\boxed{\frac{z^{2}(y^{2}-1)}{y^{2}}}$