Equation of a line passing through a point (x_{1} , y_{1}) 
y = mx + ( y_{1} − mx_{1}) 
y − y_{1} = m(x − x_{1}) 

Equation of a line passing through two points (x_{1} , y_{1}), (x_{2} , y_{2}) 

Equation of a line perpendicular to a given slope m and passing through a point (x_{p} , y_{p}) 

Equation of a line perpendicular to a line which is defined by two points (x_{1} , y_{1}) and (x_{2} , y_{2}) and passing through the point (x_{p} , y_{p}) 

Equation of a line passing through the intercepts x_{i} , y_{i} 

x_{i}y = −y_{i}x + x_{i}y_{i} 

Equation of a line passing through the point (x_{p} ,y_{p}) and parallel to a line which is defined by two points (x_{1} , y_{1}) and (x_{2} , y_{2}) 

Equation of a line parallel to the line Ax + By + C = 0 and at a distance d from it. 

Equation of the midline between the lines Ax + By + C = 0
Dx + Ey + F = 0


Equation of a line perpendicular to the line Ax + By + C = 0 

Equation of a horizontal line 

y = b 

Equation of a vertical line 

x = a 
