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Homework Statement
In my calc book, they're calculating the integral of a specific parametric equation.
Homework Equations
The rest of the question is fine, im just having trouble with these 2 lines.
I dont understand how cos^2(theta became 1/2(1+ cos2(theta))
Is this a trig relation that im missing somewhere? If so, they should at least reference it at that step, as opposed to expecting us to memorize and recognize like 50 relationships... Otherwise, i'm lost...
As a side note, i've been looking through trig relations online but cant seem to find any mention of this one, so it makes me feel like im missing something
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