cosine function

1. TRIGONOMETRY
Trigonometry is the study of measurement in triangles. Trigonometric
functions are defined as lengths in triangles as the angle in the triangle
increases. Angles are defined by circles. So the triangle increases in size in a
circle. So, the trigonometric functions are commonly called circular functions.

1
The circle has a radius
of 1 unit, so the right
angled triangle has a
hypotenuse of 1 unit.
1
-1
-1
90
180
270
0
As this is a right angled
triangle,
hyp
adj
Cos 

adj
adj

1
Therefore 
Cos
adjacent 

2. We can read off the graph
that the adjacent side of
the triangle will be 0.5.
5
.
0
120 
Cos
adj
Cos 

5
.
0
120 
Cos
As the angle increases, and
we move around the
graph, the value of the
adjacent side changes

3. 1
1
-1
-1
90
180
270
0
Cosine is called a circular repeating function. As increases, the value of
changes from 1 through -1 and back to 1. Once the angle has gone through 360 the
value of repeats.
 
Cos

Cos
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4. 1
-1
0
90
 0
90 0
180 0
270 0
360 0
450
We can see that as the value of increases the value of moves between -1
and 1.
 
Cos

Cos
y 
The period of the graph is 360 , that means the graph repeats itself every 360
Reading off values will give us information as follows: and
0
900

Cos 1
1800


Cos