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在初中平行四边形、勾股定理与解三角形[1][2]教学中,教师一般都会介绍并证明如下结论:[定理]平行四边形四边的平方和等于两条对角线的平方和.
In junior high school parallelogram, Pythagorean theorem and solution triangle [1] [2] teaching, teachers generally introduce and prove the following conclusion: [Theorem] The square sum of four sides of the parallelogram is equal to the sum of squares of two diagonal lines.