ce maths

(1/x² + 1/y²) / (1/x +1/y )

(y²/x²y² + x²/x²y²) / (y/xy +x/xy )

= [(x² + y²)/x²y²] / [(x + y)/xy]

= [(x² + y²)/x²y²] * [xy/(x + y)]

= (x² + y²) /xy(x + y)

2011-07-18 20:52:55 補充：
發問時，點數已付出。刪除答案，只會損人不利己。

2011-07-22 00:35:48 補充：
謝謝樓下的坦白，連抄襲我也註明出處。

(1/x² + 1/y²) / (1/x +1/y )

=(y²/x²y² + x²/x²y²) / (y/xy +x/xy )

= [(x² + y²)/x²y²] / [(x + y)/xy]

= [(x² + y²)/x²y²] * [xy/(x + y)]

= (x² + y²) /xy(x + y)