special hammer-like instrument

This paper introduced a few ordinary forms of t he cutting tools of lawn digging holes.

介绍了打洞刀具的几种常见形式,从刀具的入土形式和刀具的滚动形式两方面对打出洞的质量进行了分析,确定了刀具运动的理想曲线。

By structuring three-element linear regression etluation,appling the methods ofholing a matrix and block matrix inversion,the autho;deduces two-element partial regressionequation square sum and other calculus results,expounds their relation significance using vec-tor and vector projection.

通过三元线性回归方程的建立过程，运用矩阵“打洞”，分块矩阵求逆等方法推出两个偏回归平方和等结果，并利用向量以及投影阐述各量之间的关系。