Transcript Consecutive Interior angles theorem by Ross Pillischer

Finding if lines are parallel
or perpendicular
In this lesson we are trying to find
whether a 2 lines are parallel or
perpendicular on the coordinate plane.
 You can find if they are parallel if the
slopes of the two lines are the same.
 You can find if they are perpendicular if
the slopes are opposite inverse.
Ex of opposite inverse: (1/2)

Rules and Formulas
Parallel rule: the lines are parallel if the
slopes are the same.
Ex: y = 2x+3 || to y = 2x+ 7
 Perpendicular rule: The lines are
perpendicular if the slopes are opposite
inverse.
Ex: y = 2x+ 4  y = -1/2x+ 10

Examples
State if these two equations are parallel or perpendicular.
1. Y= 1/2x+ 4 and -2x+y = 6
2. Y= 5/3x- 1 and 4+y = 5/3x
3. Y= 2/3x and -3/2x+1 = Y
Answers: 1. Perpendicular 2. Parallel
3. Perpendicular
Web Links

http://hotmath.com/help/gt/genericalg1/s
ection_12_2.html
http://www.terragon.com/tkobrien/algebra/topics/parallell
ines/parallellines.html

http://www.purplemath.com/modules/slo
pe2.htm
Consecutive Interior angles
theorem
by Ross Pillischer
QuickTime™ and a
decompressor
are needed to see this picture.
(angle d and
angle e are
consecutive
interior angle
theorem)
The consecutive interior angle theorem is a
way to show lines are parallel. If two sameside interior angles are supplementary then
their two lines are parallel. My goal is to
help you understand the consecutive
interior angle theorem and see why these
lines are parallel.
Rules and Formulas

If there are two interior angles, they first must
be shown supplementary.
 When shown supplementary, it shows that the
lines the lie on are parallel.
 This process is usually used to show if two
lines are parallel.
 There is no real formula for this, it is just a
theorem.
Three Problems…




1. Line k and line l are parallel. If angle 4 is 110
degrees, what is angle 6? Answer: angle 6 is 70
degrees.
2. Angle 4 = 5x and angle 6 = 3x+ 25. Are the two
lines k and l are parallel.Answer: No, because the
interior angles are above 180 degress.
3. Line k and line l are parallel. Angle 6 is 25 degrees.
What is angle 4?
Answer: angle 4 is.
Helpful Websites

QuickTime™ and a
decompressor
are needed to see this picture.
http://hotmath.com/hotmath_help/topics/cons
ecutive-interior-angles-theorem.html
 http://www.mathsisfun.com/geometry/consecu
tive-interior-angles.html
 http://www.mathwords.com/a/alternate_interio
r_angles.htm
 Bye.