The problem is cos(-π/4+401π) is equal to (blank), if you don't understand, cos(-pi/4+401pi). I think the first step is cos(-π/4+(2x200)π+1)
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Hey OfficeSnail. What is the rule about cos(x + pi) and cos(x + 2*pi) and how can you get cos(x + 400*pi + pi) in terms of cos(x) or sin(x)?
Look office snail, you can write $\displaystyle cos(401\pi + \frac{-\pi}{4}) = cos(400\pi + \frac{3\pi}{4}) = cos(2\pi*200 + \frac{3\pi}{4}) $.
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