# Writing Equations of Parallel Lines

### {{ 'ml-heading-theory' | message }}

Linear functions are a family of functions that all have a constant rate of change. There are additional ways that pairs of lines can relate. One such way is if the lines are parallel. In this section, what makes two lines parallel, and the ways in which the rules and graphs of parallel are similar, is explored.

## Parallel Lines

Lines in the same plane that never intersect are called parallel lines. Lines are parallel if and only if they have the same slope. It follows, then, that all horizontal lines are parallel to one another, as are all vertical lines. Two lines written in slope-intercept form, $y=mx+b,$ are parallel if their slopes, $m,$ are equal and they have different $y$-intercepts, $b.$

$m_1 = m_2 \quad \text{and}\quad b_1 \neq b_2$

## Exercises

{{ 'mldesktop-placeholder-grade' | message }} {{ article.displayTitle }}!

{{ exercise.headTitle }}

*settings_overscan*

{{ 'mldesktop-selftest-notests' | message }} {{ article.displayTitle }}!

{{ tests.error }}

## {{ 'ml-heading-exercise' | message }} {{ focusmode.exercise.exerciseName }}

*keyboard_backspace*

{{ 'ml-tooltip-premium-exercise' | message }}

{{ 'ml-tooltip-recommended-exercise' | message }}

Programmeringsuppgift | {{ 'course' | message }} {{ exercise.course }}

*keyboard_backspace*{{ 'ml-btn-previous' | message }}

*keyboard_backspace*