什么是菱形

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棱形和矩形都是特殊的平行四边形。

一、棱形：①有一组邻边相等的平行四边形是棱形。

（定义）②棱形是轴对称图形，有两条对称轴。

③棱形的性质：四条边相等，对角线互相垂直。

④棱形的判定：a、对角线互相垂直的平行四边形是棱形；b、四边相等的四边形是棱形。

⑤棱形的面积等于两条对角线乘积的一半。

二、矩形：①有一个角是直角的平行四边形是矩形。

（定义）②矩形的性质：四个角是直角，对角线相等。

③在矩形中，直角三角形斜边上的中线等于斜边的一半。

④矩形的判定：a、对角线相等的平行四边形是矩形。

b、有三个角是直角的四边形是矩形。