1.  The distance between $P(x_1, y_1)$ and $Q(x_2, y_2)$ is $√{(x_2-x_1)^2+(y_2-y_1)^2}$

2.  The distance of a point $P(x, y)$ from the origin is $√{x^2+y^2}$

3.  The coordinates of the point $P(x, y)$ which divides the line segment joining 
   the points  A$(x_1,  y_1)$  and  B$(x_2,  y_2)$  internally  in  the  ratio  $m_1    :  m_2$    are
     $({m_1 x_2   + m_2 x_1}/{m_1  +  m_2},{m_1 y_2   + m_2 y_1}/{m_1  +  m_2})$
	
4.  The mid-point of the line segment joining the points $P(x_1, y_1)$ and $Q(x_2, y_2)$ is
     ${x_1+x_2}/2,{y_1+y_2}/2$
	 
5.  The area of the triangle formed by the points $(x_1, y_1)$, $(x_2, y_2)$ and $(x_3, y_3)$ is
     the numerical value of the expression 
	 ${1/2}{[x_1 (y_2 - y_3) + x_2 (y_3 - y_1) + x_3 (y_1 – y_2)]}$