## Introduction

When we found **unknown trigonometric function** or **trigonometric function of some unknown function** in at least one member of an equation we say this equation is **trigonometric**

## Examples

1) sin x + cos x = and sin 2x = cos^{2} x **are** trigonometric equations.

2) x + (tg 30 °). x^{2} e x + sen 60º = **they are not** trigonometric equations.

We say that ** r** is ** root** or ** solution** of the trigonometric equation f (x) = g (x) if **r** is a domain element of ** f ** and ** g** and if f (r) = g (r) is true.

In the equation sen x - sen = 0, for example, the numbers are some of its roots and the numbers they are not.

The set **s** of all the roots of the equation is your **solution set** or **True set.** Almost all trigonometric equations, when properly treated and transformed, can be reduced to at least one of the following three equations:

sen x = sen a

cos x = cos a

tg x = tg a

These are the **elementary trigonometric equations** or **fundamental trigonometric equations.**