Answer

We see here that 4 pi radians is an angle whose terminal side lies on the x-axis and our reference angle is exactly 0 radians. Hence, we really do not have a triangle with which to work. However, we can see that our values of x, y, and r can be taken as x=1, y=0, and r=1. Then we have the following values for the trig functions:

[trig values]

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James A. Sellers