tolong di jawab pakai cara!

Penyelesaian: 

petunjuk: x - y = [tex]( \sqrt{x} + \sqrt{y} ) ( \sqrt{x} - \sqrt{y} )[/tex]

[tex] \frac{x^-1 - y^-1}{x^1/2 + y^1/2} [/tex]
= [tex] \frac{ \frac{1}{x} - \frac{1}{y} }{ \sqrt{x} + \sqrt{y} } [/tex]
= [tex] \frac{ \frac{y - x}{xy} }{ \sqrt{x} + \sqrt{y} } [/tex]
= [tex] \frac{y - x}{xy ( \sqrt{x} + \sqrt{y} )} [/tex]
= [tex] \frac{(y - x)}{ \frac{xy (x - y)}{( \sqrt{x} - \sqrt{y} )} } [/tex]
= [tex] \frac{-(x - y)}{ \frac{xy (x - y)}{ \sqrt{x} - \sqrt{y} )} } [/tex]
= [tex] \frac{-( \sqrt{x} - \sqrt{y} )}{xy} [/tex]
= [tex] \frac{ \sqrt{y} - \sqrt{x} }{xy} [/tex]   (B).