Write the equation for a line that is a parallel or perpendicular to a line given in slope-intercept form and goes through a specific point.

Given line A and point P, Sal finds the equation of the line perpendicular to A that passes through P.

Use the equations of a pair of lines to decide whether they intersect or not. If yes, are they perpendicular? If no, are they distinct or the same line?

Learn Geometric constructions: perpendicular bisector Geometric constructions: perpendicular line through a point on the line Geometric constructions: perpendicular line through a point not on the line

Sal finds the equation of a line perpendicular to a line given in slope-intercept form that passes through a specific point.

If slopes are the same then the lines are either equivalent (both equations describe the same line) or parallel (and thus do not intersect). Two lines with different slopes will always intersect.

The equation of a straight line is y=mx+c, where m is the slope. Parallel lines have the same slope and perpendicular lines have the opposite reciprocal (flip fraction and times by -1).

We're asked which of these lines are parallel. So they give us three equations of three different lines and if they're parallel, then they have to have the same slope.

Practice Up next for you: Identify parallel and perpendicular lines Get 5 of 7 questions to level up!

In order to write its equation, all we need to know is where it crosses the X-axis and we call that point c, giving us the equation x = c. So, for example, x = -4 would be a vertical line crossing the X-axis at -4