Most shapes are made up of a number of lines (shapes like circles aren’t really made up of lines). When two lines meet they form an angle.
You need to know some special words that describe angles in order to understand all of the geometry questions on the GED math test.
The vertex of an angle is the point where the two lines meet and/or cross.
Angles are measured in degrees. Angles are between 0 degrees and 180 degrees. Degrees are often represented by the symbol °. So 180 degrees = 180°. A right angle is an angle that is exactly 90°.
Angles that are less than 90° are called acute angles.
Obtuse angles are greater than 90°.
A straight line, of course, does not have an angle. However you can say that a straight line is 180°.
Referring to Angles
On the GED math test when a question is asking you about a certain angle, the question could refer to that angle in two different ways. Both ways will use the symbol ∠ when referring to angles.
If the angles have letters at the ends of the lines and at the vertex those letters will be used to refer to the angle. The angle in the image above, for example, may be referred to either as ∠ABC or ∠CBA. The order of the letters doesn’t matter, but the vertex, in this case B, needs to be in the middle.
The other way to refer to an angle is just by the single letter or symbol next to the angle. In the example above it would be referred to as ”∠x” or “m of ∠x”, which means the “measure of ∠x.”