Cosinus

cos is adjacent / hypotenus

And, it is cosine not cosinus

Maybe remember

some old hags sin=o/h
cant always hide cos=a/h
their old age tan=o/a

<cos is adjacent / hypotenus
<
<And, it is cosine not cosinus
<
<Maybe remember
<
<some old hags sin=o/h
<cant always hide cos=a/h
<their old age tan=o/a

Those only work in a right triangle and for angles that are greater than 0 and less than 90 degrees.
for all real numbers all the trigonometric functions are defined by a unit circle:
http://web2.0calc.com/geometry/obVmliFoOm.png

So the formula for cosine is the point in the unite circle shown in the picture...

Sorry. I put the sin(x) and cos(x) wrong way around in the picture.....