It is easy if you know how sin and cos behave.
Here you can see that sine and cosine are exactly the same wave, with the exception that the cosine is moved half a period to the left (or right, it doesn't matter as they are infinite.)
So you see that at x=0, sin(x)=0 and cos(x) = 1
This would mean that the answer closest to zero would be the smallest step.
So now all we need to know is the difference between radians and degrees.
Here we see that a full circle is 180 degrees and 2pi (which is about 6.3) radians.
So we know that 1 radian is more than 1 degree (1/6.3 is larger than 1/180), meaning that the smallest answer (the one closest to zero) is in degrees and the other one is in radians.
Now, knowing all this it is very easy to check if you are using radians or not.
Just fill in sin(pi/2). In degrees it will be almost zero and in radians it will be 1.
I hope that this helped!
The beginning of knowledge is the discovery of something we do not understand. - Frank Herbert
Science without religion is lame, religion without science is blind. - Albert Einstein
Knowledge is a powerful weapon, but only when its user can wield it.