Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.1 6/24/83; site fortune.UUCP Path: utzoo!watmath!clyde!burl!we13!ihnp4!fortune!rpw3 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 Sender: notes@fortune.UUCP Organization: Fortune Systems, Redwood City, CA Lines: 23 #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 UUCP: {sri-unix,amd70,hpda,harpo,ihnp4,allegra}!fortune!rpw3 DDD: (415)595-8444 USPS: Fortune Systems Corp, 101 Twin Dolphins Drive, Redwood City, CA 94065