2. Explanation October 4, 2012
A straight line that crosses parallel lines is called the
transversal.
Angles at the same position are equal.
These are equal corresponding angles. They are in the
same position between the transversal and each parallel
line.
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3. Explanation October 4, 2012
Alternate angles are on opposite sides of the transversal
and are equal.
You can think of a ‘Z’ shape to help you remember this.
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4. Explanation October 4, 2012
Interior angles are angles inside the parallel lines, on the
same side of the transversal.
The sum of interior angles is always 180º.
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5. Example October 4, 2012
If angle a is 120º,what is angle b?
a 120º
120º
b
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6. Example October 4, 2012
If angle a is 60º,what is angle b?
a 60º
60º
b
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7. Example October 4, 2012
If angle a is 72º,what is angle b?
a 72º
72º
b
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8. Example October 4, 2012
If angle a is 120º,what is angle b?
a 120º
120º
b
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9. Examples October 4, 2012
What is angle d?
125º
55º
d
What is angle r?
41º
139º
r
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10. Explanation October 4, 2012
You may need to use your knowledge of both parallel
lines and triangles in a single question.
Angles are often labelled with single, lower case letters.
They may also be identified using upper case labels at
the ends of the lines.
You can also identify lines this way.
A
x z
32º R Line AR
57º
y
91º
Angle ACB
32º
B C
If angle ACB is 32º and angle y is 91º, what is angle x?
32 + 91 + 57 = 180
?
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End
