# Evaluating Trigonometry For Special Angles

In these lessons, we will learn
the trigonometric functions of the special angles 30˚, 45˚, 60˚, and 90˚ and how to use them to find exact values of trigonometric expressions.

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## Special Angles: 30 and 60

Let us first consider 30˚ and 60˚.

These two angles form a 30˚-60˚-90˚ right triangle as shown.

The ratio of the sides of the triangle is

From the triangle we get the ratios as follows:

## Special Angles: 45 and 90

Next, we consider the 45˚ angle that forms a 45˚-45˚-90˚ right triangle as shown. The ratio of the sides of the triangle is

Combining the two tables we get:

* Example: *

Evaluate the following without using a calculator:

a) 2 sin 30˚ + 3 cos 60˚ – 3 tan 45˚

b) 3(cos 30˚)^{2} + 2 (sin 30˚)^{2}

* Solution: *

a) 2 sin 30˚ + 3 cos 60˚ – 3 tan 45˚

b) 3(cos 30˚)^{2} + 2 (sin 30˚)^{2}

## Videos

This video shows how to find the trig ratios of the special angles and how to use them to find exact values of expressions involving sine, cosine and tangent values of 0, 30, 45, 60 and 90 degrees. This is the first part of a two part lesson.

This lesson shows how to find the trig ratios of the special angles and how to use them to find exact values of expressions involving sine, cosine and tangent values of 0, 30, 45, 60 and 90 degrees. This is conclusion of a two part lesson.

30-60-90 and 45-45-90 Triangles.

The following video explains how the trigonometry values for the special angles are obtained.

(Errata: At time 4:10, the video should show that ).

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