Question

How to tell if two lines are perpendicular

Answer 1

They'll be negative reciprocals.

Explanation:

A pex :)

Answer 2

The two lines are perpendicular if
`m_1 * m_2 = - 1`

EXPLANATION

Given two lines:

`y=m_1x+b_1`

and

`y=m_2x+b_2`

We can tell wether these two lines are perpendicular to each other using their slopes.

If the product of their slopes is -1, the then the two line are perpendicular.

For example:

The line

`y = 2x + 6`

has slope

`m_1= 2`

and the line

`y = - (1)/(2) x + 1`

has slope

`m_2 = - (1)/(2)`

The product of the two slopes is

`m_1 * m_2 = 2 * - (1)/(2)`

This implies that:

`m_1 * m_2 = - 1`

Therefore the two lines are perpendicular.