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May 23rd, 2009, 03:12 PM   #1
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trigonometic sine wave equation, Help guys please !

Hi guys,

I got a math assignment due on Tuesday and am really stuck with no on to help me around.

v1 = 20sin(theta -30)
v2 = 30sin(theta +45)
vr = v1 + v2

question 1)

1)plot v1,v2 and vr in the same graph
2)resultant equation should be written in the form of vr=Asin (theta + betha)
3) express 20sin ( theta-30) + 30sin (theta +45) in the form of Rsin (theta + alpha)

this is the question , i can graph v1 and v2, but for vr , should i just put in values and add them ?
and for 2 and 3 i don't how can i do the conversion ?

any help is appreciated , thanks .
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May 23rd, 2009, 04:20 PM   #2
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Re: trigonometic sine wave equation, Help guys please !

Short tutorial:

I'll use capitals for known and x for unknown.
You have terms of the form Asin(x+B)
sine law gives you AcosBsinx+AsinBcox, where sinB and cosB are known.

Add terms to get vr and you will have Msinx+Ncosx, where M and N are known. Now let L=(M^2+N^2)^1/2. So (M/L)^2 + (N/L)^2 = 1. Therefore M/L and N/L are cos and sin of a known angle C. vr=Lsin(x+C).
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