y=-x+8x+y=8说明直线的法方向是(1,1)法方向单位向量是(1/2^(1/2),1/2^(1/2))直线方程又可写成：x/2^(1/2)+y/2^(1/2)=8/2^(1/2)=4*2^(1/2)这可理解成向量(x,y)与向量(1/2^(1/2),1/2^(1/2))的数量积(又称点积或内积)等...