Question regarding Cosine Function

[F1225]

Do anyone know what properties of cosine function should we use? and the method to use it? kinda blur...

 

[Simon Bridge]

The cosine is the ratio of the adjacent side of a right-angled triangle to it's hypotenuse.
If you sketch a graph of the cosine function, you see it obeys the first relation ... that's the "well known properties" that they are talking about. The second relation actually follows from the properties of a square (the power of two).

Sketch them and you'll see.

 

[F1225]

Thanks...I finally got it. Square of any function must be greater or equal to 0...

 

[Simon Bridge]

Well done :)