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maths .urgent.......

發問:

1/x^2+1/y^2 divided by 1/x+1/y 更新: The ans is 1/x^2-1/xy+1/y^2 更新 2: How to calculate this question?thx...

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圖片參考：http://i1096.photobucket.com/albums/g340/pingshek/2013-02-11_zps7449033a.png?t=1360560470 http://i1096.photobucket.com/albums/g340/pingshek/2013-02-11_zps7449033a.png?t=1360560470 2013-02-11 13:35:21 補充： Similarly, (1/x2 - 1/y2) ÷ (1/x + 1/y) = (y2/x2y2 - x2/x2y2) ÷ (y/xy + x/xy) = (y2 - x2)/x2y2 ÷ (y + x)/xy = (y + x)(y - x)/x2y2 * xy/(y + x) = (y - x)/xy 2013-02-11 13:35:31 補充： Similarly, (1/x2 - 1/y2) ÷ (1/x - 1/y) = (y2/x2y2 - x2/x2y2) ÷ (y/xy - x/xy) = (y2 - x2)/x2y2 ÷ (y - x)/xy = (y + x)(y - x)/x2y2 * xy/(y - x) = (x + y)/xy

其他解答:

Put x = 1 and y = 2 : (1/x2 + 1/y2) ÷ (1/x + 1/y) = (1/12 + 1/22) ÷ (1/1 + 1/2) = (5/4) ÷ (3/2) = (5/4) x (2/3) = 5/6 1/x2 - 1/xy + 1/y2 = 1/12 - 1/(1*2) + 1/22 = 1 - 1/2 + 1/4 = 3/4 Hence, (1/x2 + 1/y2) ÷ (1/x + 1/y) ≠ 1/x2 - 1/xy + 1/y2|||||No,the question is (1/x^2+1/y^2)/(1/x+1/y).it is HKCEE1991 mc question 5.|||||Do you mean 1/x^2 - 1/y^2 ?