If a point X = ( x 0 , y 0 , z 0 ) {\displaystyle \displaystyle X=(x_{0},y_{0},z_{0})} lies in the plane P {\displaystyle P} , then a x 0 + b y 0 + c z 0 = d {\displaystyle \displaystyle ax_{0}+by_{0}+cz_{0}=d} .
