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高中《代数》（必修）下册第１５页第６题可改述为：（ａ２＋ｂ２）（ｃ２＋ｄ２）≥（ａｃ＋ｂｄ）２○＊当且仅当ａ／ｃ＝ｂ／ｄ时取等号．灵活巧妙地运用○＊式，可使某些三角问题简捷获解．例１已知Ａ，Ｂ都是锐角，且ｃｏｓＡ＋ｃｏｓＢ－ｃｏｓ（Ａ＋Ｂ）＝３／２，...
The sixth item in the high school algebra (required) in the second book of the 15th book can be rephrased as: (a2+b2)(c2+d2)≥(ac+bd)2○* If and only if a/c=b/d is the equal sign. Flexible and clever use of the ○* formula to make certain triangle problems easy to solve. Example 1 is known as A, B are all acute angles, and cosA+cosB-cos(A+B)=3/2,...