Sunday, November 8, 2009


Supplementary Angles:
If the sum of two angles is 180 degrees ie, if they form a straight line , the two angles are supplementary.
Each angle is called the supplement of each other.

Complementary Angles:
If the sum of two angles is 90 degrees.

Reflex Angles:
Angles larger than two right angles but less than a full circle (between 180° and 360°) are called reflex angles.

Acute Angles:
Those angles whose measure is less than 90 degrees

Obtuse Angles:
Those angles whose measure is greater than 90 degrees but less than 180 degrees.

Right Angles:
If two supplementary angles are equal, they are both right angles.
A right angle is half of a straight line and measures exactly 90 degrees.

Intersecting Lines:

When two lines intersect, four angles are formed.
Adjacent angles are supplementary and vertical angles are equal.

Vertical Angles:

Two angles opposite each other, formed by two intersecting straight lines that form an "X"-like shape, are called vertical angles or opposite angles. These angles are equal in measure.

Straight Angles:

Has its sides lying along a straight line and equal to 180 degrees.

Adjacent Angles:

Angles that share a common vertex and edge but do not share any interior points are called adjacent angles.

Parallel Lines and Transversals:

A transversal (line t) across parallel lines form four equal acute angles and four equal obtuse angles.

The top line (line l) is parallel to the bottom line (line m) and line t is the transversal.

Angles 1, 2, 5 and 8 are all equal and acute.
Angles 3, 4, 6 and 7 are all equal and obtuse.

In addition, each of the acute angles is supplementary to each of the obtuse angles. Angles 1 and 4 are supplementary, as are 2 and 3, 2 and 6, and so on.