Parallel and Perpendicular Lines

Pre AP GeometryPlease use this presentation to complete the

notes for a DIY gradeThank you

Parallel Lines• Parallel lines remain the same distance apart over their entire length. •To show that lines are parallel we draw small arrow marks on them. •Shorthand: If you want to talk about two parallel lines there is a shorthand that can be used. For example, if you want to say that line PQ is parallel to line RS you could write :

•PQǁRS•When looking at two equations parallel lines will have the SAME SLOPE.

So looking at the equations which lines would be parallel to each other?

• A) y=2x+1 y =3x+1• B) y=1/2x+5 y=1x+1• C) y=3x+1 y=3x+5

If you guessed C you are right!

• Remember: when you are looking at the form of y=mx+b…

y=mx+b

For C the slopes are the same:C) y=3x + 1

y=3x + 5

SlopeY-Intercept

Perpendicular Lines

• Perpendicular lines are two lines that meet at a right angle.

• To write that line AB is perpendicular to line CD. – AB CD

• When looking at two equations perpendicular lines have opposite and reciprocal slopes.

A B

C

D

Looking at the equations which pair of lines are perpendicular?

• A) y=2/3x+1 y= 3x +2 B) y= 4x+2 y= 4x+5 C) y=2x+1 y=2x+1 D) y= 1/2X+2 y =-2X+2

D is Correct!

• Remember we are interested in the slopes– Y=1/2x + 2– Y=-2x + 2

• So since ½ is positive we want a negative• Now if you flip ½ over you will get 2/1 which is

the same thing as 2.– So we get -2

Skew Lines

• Non-Coplanar lines that do not Intersect.

Not on the same plane