Why Is My Integral Result Incorrect for Cosine of 2 Theta?

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SUMMARY

The integral of cosine of 2 theta from pi minus theta1 to pi plus theta1 results in positive one half sine of 2 theta1, which is incorrect. The correct result should be negative one half sine of 2 theta1 due to the orientation of the vector involved in the calculation. The mistake was identified as stemming from an incorrect vector orientation, necessitating a reversal of the vector direction to achieve the correct integral result.

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Homework Statement



From angles pi minus theta1 to pi plus theta1, what is the integral of cosine of 2 theta times d theta?

Homework Equations





The Attempt at a Solution



When I evaluate this definite integral from pi minus theta1 to pi plus theta1, I get positive one half sine of 2 theta1.
It should be NEGATIVE one half sine of 2 theta1.

Is 2pi + 2theta1 and 2pi - 2theta1 somehow wrong?
 
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Hi PieOperator! :smile:

(have a pi: π and a theta: θ and an integral: ∫ and try using the X2 tag just above the Reply box :wink:)

you should have got [1/2 sin2θ]π-θ1π+θ1

what happened then? :confused:
 
Thanks. I found my mistake. It has to do with vectors and the correct orientation. It is positive one half sine of 2 theta in the incorrect vector orientation. I just have to reverse the direction of the vector, and the interval reverses as well.
 

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