How would you decide which calculator is using readians and which calculator is using degrees? Suppose you have borrowed two calculators from friends, but you do not know whether they are set to work in radians or degrees. Thus you ask each calculator to evaluate sin 1. One calculator replies with an answer of 0.017452; the other calculator replies with an answer of 0.841471. Without further use of a calculator, how would you decide which calculator is using readians and which calculator is using degrees?
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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!