SQL Inverse Trig Functions

[chili5]

I was looking more into functions in SQL and found the trig functions. Something just doesn't seem right though. I don't get how the inverse functions work?

If I use the cosine function, it takes an argument representing an angle in radians.

So:

SELECT COS(5.5);

Is the cosine of an angle which is 5.5 radians. Thus the resulting value is:

0.70866977429126

Now, if I was to apply ACOS to 0.70866977429126 then the resulting value should be 5.5?

So what we should have is:

SELECT ACOS(COS(5.5));

The resulting value should be:

5.5

Then why is it

0.783185307179586

? I'm sure I'm missing something. Any thoughts as to what I am missing here?

[WingedPanther]

COS is a many to one function. The result is that it doesn't have an inverse that is guaranteed to result in the original value entered.

ACOS returns a value between 0 and PI.

[chili5]

So then is that the same as SIN and ASIN because those create weird results also.

SELECT ASIN(SIN(3.5));

returns -0.358407346410207.

When I do:

SELECT ATAN(TAN(3.5));

The result is 0.358407346410207. Then what are these functions doing? Where are these weird numbers coming from?

When I do this:

SELECT DEGREES(ASIN(SIN(RADIANS(3.5))));

I get the original value of 3.5. I don't actually know what a radian is. Does that mean I can't have 3.5 radians? Which is why I am getting weird results?

[WingedPanther]

In advanced math and ALL programming languages, trig is done in radians. A circle has 2*PI radians (360 degrees). 90 degrees is PI/2 radians. If you are thinking in degrees, you will get severely scrambled.