Why Vector3.Angle return an angle in degrees?

I need an angle in radians because Mathf.Cos needs it.
In Vector3.Angle’s source code, the value translates from radian to degree.

I don’t want to translate radian to degree to radian.

Is there any way to get an angle in radians directly?

Just multiply the result by Mathf.Deg2Rad constant. Or, if you really think that those two multiplications will make your program slower, copy that code and remove the conversion at the end.

I wonder if some JIT optimizations would remove those two constant multiplications completely. But really, unless it reaaally matters, just convert it back.

I know.
I want to ask you why I have to do it.
Why Vector3.Angle’s returns an angle in degree?