Introduction to basic trig functions

In any right angled triangle, for any angle:

The sine of the angle = the length of the opposite side   
                                         the length of the hypotenuse
sin x= O/H   
   
The cosine of the angle = the length of the adjacent side
                                             the length of the hypotenuse

cos x= A/H

The tangent of the angle = the length of the opposite side

                                               the length of the adjacent side

tan x= O/A


More Study:

Six Trigonometric Functions
Area of Triangle and Parallelogram Using Trigonometry

Two Special right Triangles

Special triangle:
45-45-90



30-60-90

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More study:
Special Triangle

The Triangle Angle Bisector Theorem