知识点1 两点距离公式
设$P_{1}(x_{1},y_{1})$,$P_{2}(x_{2},y_{2})$之间的距离:
$|P_{1}P_{2}|$=$\sqrt {(x_{2}-x_{1})^2+(y_{2}-y_{1})^2}$.
知识点2 两点中点坐标计算
设$P_{1}(x_{1},y_{1})$,$P_{2}(x_{2},y_{2})$,$P$为$|P_{1}P_{2}|$线段的中点,则:
$P$=($\frac{x_{1}+x_{2}}{2}$,$\frac{y_{1}+y_{2}}{2}$).
点$P_{0}(x_{0},y_{0})$到直线$Ax+By+C$的距离$d$为:
$d$=$\frac{|Ax_{0}+By_{0}+C|}{\sqrt{A^{2}+B^{2}}}$.
两条平行直线$Ax+By+C_{1}=0$与$Ax+By+C_{2}=0$之间的距离为:
$d$=$\frac{|C_{1}-C_{2}|}{\sqrt{A^{2}+B^{2}}}$.