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    Sin60= (surd)3/2

    so what is the value of sin120?
    sin 240?

    Please help me as to how to do this!!
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    Use the symmetry of the sin graph about 90 and 270. You know that 60 degrees is the same distance from 90 degrees as 120 degrees. And then extend that for 240 degrees but it's negative this time
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    I agree with mattypb, draw the graph and think carefully about the symmetry of the sinewave.

    If you prefer a more algebraic way of doing things, try using the sine double-angle rule (if you've learned it).

    Failing all this - cheat!
    Type it into a calculator and see what you get! Is this answer what you'd expect? Why?
 
 
 
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