Trigonometric formulas (please help)

zee

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Jan 15, 2006
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How do I simplify the given equation?


sin 3x cos 2x - cos 3x sin 2x



Thank you
 
Hello, zee!

How do I simplify the given equation expression ?\displaystyle \text{How do I simplify the given }\sout{equation}\text{ expression ?}

      sin3xcos2xcos3xsin2x\displaystyle \;\;\;\sin3x\cdot\cos2x\,-\,cos3x\cdot\sin2x
The quickest way is to recognize the compound-angle formula:

    sin(AB)  =  sin(A)cos(B)cos(A)sin(B)\displaystyle \;\;\sin(A\,-\,B)\;=\;\sin(A)\cdot\cos(B)\,-\,\cos(A)\cdot\sin(B)


We are given the right side of the formula with: A=3x,  B=2x\displaystyle \,A\,=\,3x,\;B\,=\,2x

Answer: sin(AB)  =  sin(3x2x)  =  sinx\displaystyle \,\sin(A\,-\,B)\;=\;\sin(3x\,-\,2x)\;=\;\sin x
 
Hey- for this one you should use the trigonometric sum and difference identiy:


Sin(x-y) = sinxcosy - sinycosx

therefore, if you have sin3xcos2x - cos3xsin2x, it can be simplified into the above equation.
 
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