13.3 Parallel and Perpendicular Lines

Parallel Lines Coplanar lines that do not intersect

Theorem Two nonvertical lines are parallel if and only if their slopes are equal

Perpendicular lines

Theorem Two nonvertical lines are perpendicular if and only if the product of their slopes is -1.

In english That means that the slopes of two perpendicular lines are –Opposite (one + and one -) –Reciprocals ( and )

White Board Practice r || s and r  t Slope of rSlope of sSlope of t

White Board Practice r || s and r  t Slope of rSlope of sSlope of t

White Board Practice r || s and r  t Slope of rSlope of sSlope of t

White Board Practice r || s and r  t Slope of rSlope of sSlope of t

White Board Practice r || s and r  t Slope of rSlope of sSlope of t

White Board Practice r || s and r  t Slope of rSlope of sSlope of t

Remote Time The slopes of two lines are given. Are the lines A: Parallel B: Perpendicular C: Neither D: I don’t know

A: Parallel B: Perpendicular C: Neither D: I don’t know

White Board Practice Use slopes to show that a quadrilateral with vertices A(-2,7), B(3,7), C(6,11), and D(1,11) is a parallelogram.