# How do you find the equation of a normal line if you know the equation of the tangent line?

Oct 19, 2014

If a tangent line has the equation

$y - {y}_{1} = m \left(x - {x}_{1}\right)$,

then the normal line at the point of contact is

$y - {y}_{1} = - \frac{1}{m} \left(x - {x}_{1}\right)$.

I hope that this was helpful.