3'13'3 Parallel Lines and Slopes

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3.1-3.3 Parallel Lines and Slopes

• Obj identify relns b/t parallel lines,
  transversals, and angles. Also, find the slopes
  of lines.

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Defns

• Parallel Lines coplanar lines that do not
  intersect
• Depicted by
• In a diagram, small triangles drawn on the line
  indicate parallelism
• Transversal a line that intersects two or more
  lines in a plane at different points

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Congruent Angles from Lines
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More Congruent Angles
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Last theorem before trying it out.
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Example TBD in class
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What about variables?
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Draw your own lines..(pg. 151)
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As crazy as it gets. (pg. 152)
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3.3 Slopes

• Slope steepness of a line, or rise over run

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How to find slope

• Walk the line
• Find two points on the line
• Start at the one on the left
• Count up () or down (-), then run to the right

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Walking the line
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Or, use the formula
Example Find the slope of the line that passes
through (1,2) and (-4,1)
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Special slopes of lines

• Parallel lines have the SAME slope
• Perpendicular lines have opposite reciprocal
  slopes.
• Vertical lines never RUN, so they have an
  undefined slope.
• Horizontal lines never RISE, so they have a zero
  slope.

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Rate of Change

• Same thing as slope, but we measure a change over
  a period of time
• Ex. In 2003, 20 million songs were legally
  downloaded from the internet. In 2004, 200
  million songs were legally downloaded. If this
  increases at the same rate, how many songs will
  be legally downloaded in 2008? (pg 158)

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Determine whether the lines are parallel,
perpendicular, or neither

• Find the slope of each line and compare
• Ex. Line 1 passes through (-1,2) and (2,3)
• Line 2 passes through (0,0) and (3,1)

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SAT practice
Question 1 Four distinct lines lie in a plane,
and exactly two of them are parallel. Which of
the following could be the number of points where
at least two of the lines intersect?1. Three2.
Four3. FiveA. I onlyB. III onlyC. I and II
onlyD. I and III onlyE. I, II, and III
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Finally..