for all these types of triangles，we have only one formula to calculate its area，whereas we have learned that all different types of quadrilateral，have different formula for their areas，isn't this little unfair for triangles。
宋元时期，中国数学迎来了一个辉煌高峰，涌现了一批卓越的数学家，秦九韶就是其中的杰出代表。他与李冶、杨辉和朱世杰并称“宋元数学四大家”，所著《数书九章》被誉为数学史上的经典之作，取得的很多成就具有世界性意义。
