Expert: Steve Holleran - 9/11/2008

Question
Why does y=sin(x) return a non zero number when x=360 or x=2pi or x=6.283185307 Radians. Also why when 360 = 2pi does the sin function of 360 return the value of 0.9589 and the sin function of 2pi return a value of -2.4502. I am looking for a formula that i can plot a sin wave starting from 0,0, rising to a peek, lowering to a troth, and returning to 0 in 2pi or 360 degrees.

Thank you for your time and sharing your knowledge
Chris  

Answer
Hi Chris,

This is a common problem when using the calculator.  You have to be sure that the calculator is in the proper mode.

When evaluating sin 360 degrees, be sure the calculator is in degree mode.  If not, and it is in radian mode, you're requesting the
sine of 360 radians!

Also, when you hit sin 2pi, the calculator is finding the sin of 2 radians and multiplying it by pi.  Try putting () around the 2pi and you should get the correct answer, 0.

To get values for your graph, I would mark off units of pi/2 on the x axis and keep the calculator in radian mode to find the sine values.

Hope this solves the problem.  If not, let me know.
Steve