An
angle is defined as: where two rays or two line segments join at a common
endpoint called the vertex. See part
1 for additional information.
Acute
Angle
An acute
angle measures less that 90° and can look something like these
(angles between the grey rays):
Right
Angle
A right
angle measures exactly 90° and will look something like this:
Obtuse
Angle
An obtuse
angle measures more than 90° but less than 180° and will look
something like these:
Straight
Angle
A straight
angle is 180°
Reflex
Angle
An reflex
angle is more than 180° but less than 360° and will look something
like this:
Pairs
of Angles:
Complementary
Angles
Two
angles adding up to 90° are called complementary angles.

ABD +
DBC are Complementary 
Supplementary
Angles
Two
angles adding up to 180° are called supplementary angles.

ABD +
DBC are Supplementary 
If you
know the angle of
ABD, you can easily determine what the
DBC is by subtracting
ABD from 180!
On to Part
3.
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