using the first two terms of the Maclaurin series for y=cos(x) yields to within 0.001 over the interval |x| < k when k=
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The series for cosine is alternating, so the error is less than the next term (the third one) in magnitude, so you can have .
As an afterthought, this is a dumb multiple choice question. Why not just always pick the smallest number?
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