geometry 3.4 big idea: find the slope of a line. determine if lines are parallel or perpendicular
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Geometry 3.4Big Idea: Find the Slope of a Line.
Determine if lines are parallel or perpendicular.
Reminders:Slope = steepness of a
line
Positive Slopes: rise to right
Negative Slopes: fall to right
Zero Slopes: horizontal lines
Z
Undefined Slopes: vertical lines(No slope)
N
The greater the absolute value of the slope, the steeper the line.
Find the slope of a line that passes through(-1, 3) and (3, 2).
Find the slope of a line that passes through (-1, 1) and (2, 0).
Which line is steeper?
Postulate 17: Slopes of Parallel
LinesIn a coordinate plane,
two nonvertical lines are ║ if and only if they have the same slope. (Any 2 vertical lines are parallel.)
Postulate 18: Slopes of
Perpendicular LinesIn a coordinate plane, two
nonvertical lines are ┴ if and only if the product of their slopes is -1. (All horizontal lines are ┴ to all vertical lines.)
• Find the slope of the line that passes through (-1, 3) and (4, 1).
• Find the slope of the line that passes through (-2, -1) and (3, -3).
• Are these lines parallel or perpendicular?
• Find the slope of the line that passes through (2, 5) and (5, 3).
• Find the slope of the line that passes through (3, 0) and (7, 6).
• Are these lines parallel or perpendicular?
Graph• Graph the line through the given point with
the given slope.
-10 -9 -8 -7 -6 -5 -4 -3 -2 -1 1 2 3 4 5 6 7 8 9 10x
-10
-9
-8
-7
-6
-5
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-3
-2
-1
1
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y
Graph• Graph the line through the given point with
the given slope.
-10 -9 -8 -7 -6 -5 -4 -3 -2 -1 1 2 3 4 5 6 7 8 9 10x
-10
-9
-8
-7
-6
-5
-4
-3
-2
-1
1
2
3
4
5
6
7
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9
10
y