[IB-HL_FTPR20150402] Periodicity cos a fortiori

     In this article, I give a rigorous proof of the period of cosine functions, using an a fortiori argument, signaled by the use of the words “in particular”.  When something is generally true for, say, all real numbers, it is “all the more” true for a particular case of a real number like zero.  I use this logic to nail down the answer.

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Suitable Levels

* revision for IB Mathematics HL / SL

* other syllabuses that teach trigonometry