Triangles and Angles

An angle is measured in degrees (°). The degree of an angle runs between 0° and 180°.

Both triangles and angles are classified into three different types: acute, right and obtuse

TRIANGLES:

An acute triangle is a triangle where all three angles measure less than 90°.
Example: Angle A is 47°, Angle B is 39°, and Angle C is 12°

A right triangle is a triangle where at least one of the angles measures exactly 90°.
Example: Angle A is 68°, Angle B is 51°, and Angle C is 90°

An obtuse triangle is a triangle where at least one of the angles measures more than 90°.
Example: Angle A is 22°, Angle B is 138°, and Angle C is 44°

ANGLES:

An acute angle is an angle that measures less than 90°.
A right angle is an angle that measures exactly 90°.
An obtuse angle is an angle that measures more than 90°.

How to find the missing degree of an angle in a triangle is easy. You need to subtract the known from the sum of the three angles. If Angle A is 92° and Angle B is 31° what would Angle C be? You simply start with Angle A and subtract Angle B to get Angle C as follows:

92° - 31° = 61°

Angle C is 61° - correct? Well, not exactly because, remember, we are measuring the degree of an angle of a triangle. The three angles of a triangle must always be equal to a total of 180° (the sum of all three angles). So we need to first add together the known angles, here it is 92° and 31° and then we subtract that answer from the total of 180° as follows:

92° + 31° = 123°
180° - 123° = 57°
92° + 31° + 57° = 180°
Angle C = 57°