## Periods of Trigonometric Functions

Here are two general questions

How would you find the period of:

sin(2Pi*t)+sin(4Pi*t)

or

cos(3t)sin(2t)

Thanks
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 The first is simple it is one period of the lower frequency ( the other is a simple harmonic ) . In the second did you really mean multiply or just leave out a + sign?? I do not always find the maths simple --- my fall back to this ( to get a clue ) is to graph the function. ( But not by hand ) . I always use QBasic in which you can set up the equations and the graph in a matter of minutes . However cos(a).cos(b) == a function of a+b and a-b so one frequency is 5 and the other 1 , so the frequency compared to either of the originals is 1. That is, due to multiplication beats are formed between two frequencies Since the normal wave equation is A.Sin ( 2.pi/T.t) it , means that 2.pi/T=1 so T = 2.pi To solve these equations for T -- first compare them to the usual equation The multiplier of t is 2.pi.f for a simple wave or 2.pi/T --- then if required use the normal trig relations for compound functions . In cases of addition of sine waves there will only be a common period if the frequencies have an integer relation. The same is true for multiplications . In general there may be no period at all, or maybe extremely long. For instance cos(99.t).cos(101.t) will will have a period about 50x times greater than either . Ray.

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