Can anyone PLEASE explain axis rotation?

[m0nk3y]

So I am asked to rotate by 45 degrees about the y-axis.

With the power of the net i found that it is;
[ cos(45) 0 sin (45);
0 1 0;
-sin(45) 0 cos(45)]

i really would like to understand HOW they get this.

THANKS in advance!

 

[Doc Al]

Read this: http://www.kwon3d.com/theory/transform/rot.html"

 

[m0nk3y]

Thank you, that helped alot! I get finally get it now!