If two lines are parallel to the same line, then they are parallel to each other
If two lines are perpendicular to the same line then they are perpendicular to each other
When all right anles are congruent to each other
Right Angle Theorem
They always have the same slope
Parallel Lines
Has a slope of zero
Horizontal Lines
Have an Undefined Slope
Vertical Lines
Lines goes up to the left
Negative Slope
Line goes up to the right
Positive Slope
measures how steep the line is
Slope
Formula for Slope?
y2-y1
x_{2}-x_{1}
When is it an undefined slope?
When the zero is the numerator
In a coordinate plane, 2 non-vertical lines are perpendicular if and only if the product of their slopes is -1.
(when the slopes are opposite reciprocals)