Parallel lines ​

When two lines are parallel, they have the same gradient. So, in the below picture

we have

Perpendicular lines ​

When lines are perpendicular, they meet at a right-angle.

As we will see in a later problem, perpendicular gradients have the special property that

which is sometimes written as

(We sometimes say that $m_2$ is the negative reciprocal of $m_1$.)

Find the equation of the line passing through $(5,-1)$ parallel to the line