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From: rpw3@fortune.UUCP
Newsgroups: net.math
Subject: Re: need help - (nf)
Message-ID: <2436@fortune.UUCP>
Date: Sun, 5-Feb-84 07:03:30 EST
Article-I.D.: fortune.2436
Posted: Sun Feb  5 07:03:30 1984
Date-Received: Wed, 8-Feb-84 08:13:35 EST
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#R:mgweed:-668600:fortune:6200004:000:747
fortune!rpw3    Feb  5 01:13:00 1984

You have a formula for arc-cosine, and you have sin(x), so if you
could go from sin(x) ==> cos(x) you could arc-cos(cos(x)) and be home, eh?

Well, look at a unit circle and note that (sin(x))^2 + (cos(x))^2 = 1^2 = 1,
since the sine and cosine are the opposite and adjacent of a right triangle
of hypoteneuse (sp?) 1 (i.e., radius of the unit circle), by the Pythagorean
Theorem.

So cos(x) = sqrt(1 - (sin(x)^2).

All details of guessing which quadrant "x" was originally from are left
to the student. No way to know, from the info given. I assume here 1st 
quadrant. Don't.

Rob Warnock

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