Lines and Angles . B. A. D. l. C. m. PARALLEL LINES. Def: line that do not intersect. Illustration: Notation: l || m AB || CD. Examples of Parallel Lines. Hardwood Floor Opposite sides of windows, desks, etc. Parking slots in parking lot Parallel Parking
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Two rays or line segments that meet at a point form an angle. The point where the rays meet is called the vertex of the angle.
We measure the size of an angle using degrees.
1. by giving the angle a name, usually a lower-case letter like a or b, or sometimes a Greek letter like α (alpha) or θ (theta), or sometimes a number
2. or by the three letters on the shape that define the angle, with the middle letter being the vertex.
Example angle "a" is "BAC” (or
and angle "θ" is "BCD” (or “DCB”)
Acute – less than 90 degrees
Right – exactly 90 degrees (indicated on the GED by a square in the corner of the angle)
Obtuse – more than 90 degrees
Straight – exactly 180 degrees
Two angles are called complementary angles if the sum of their degree measurements equals 90 degrees.
One of the complementary angles is said to be the complement of the other.
Two straight lines crossing create vertical angles. Vertical angles (such as <BEC and <AED) have equal angle measurements.
In the diagram below, <AEB and <DEC are also vertical and therefore equal angles.
4 and 2
3 and 1
5 and 7
6 and 8
vertical angles. Therefore,
their measurements are the same.
<UNB = 130°
90 – 43 = 47
<ZMS = 47°
so <EKR = 38°
<EKR, so <AKE = 142° (180 – 38)
so <RTN must be 55° (180 – 125)
to <NTF, so it must also be 55°
the same measurements. <KRT = 125°
All triangles have interior angles totaling 180°,
So 180 – (52 + 48) gives us:
<BAC = 80°
interior angles totaling 360°,
so, 360 – (68+106+126)
360 – 300 = 60
gives us:angle x measures 60°