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高一数学已知lg(x+2y)+lg(x高一数学.已知lg(x+2

2010-10-20 17:51:28傈***
高一数学.已知lg(x+2y)+lg(x-y)=lg2+lgx+lgy,求x/y的值.高一数学.已知lg(x+2y)+lg(x-y)=lg2+lgx+lgy,求x/y的值. 要过程~高一数学已知lg(x+2y)+lg(x高一数学.已知lg(x+2y)+lg(x-y)=lg2+lgx+lgy,求x/y的值.高一数学.已知lg(x+2y)+lg?

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  • 参考下面这个若lg(x-y)+lg(x+2y)=lg2+lgx+lgy,求x/y的值 lg(x - y) + lg(x + 2y) = lg[(x - y)(x + 2y)] lg^2 + lgx + lgy = lg(2xy) 所以: (x - y)(x + 2y) = 2xy x^2 + 2xy - xy - 2y^2 = 2xy x^2 - 2y^2 = xy x/y - 2y/x = 1 设 a = x/y 则有 a^2 - a - 2 = 0 (a - 2 )(a + 1) = 0 a = 2,-1 ..............根据题意取正 所以:x/y = 2
    2010-10-20 18:57:23
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