Talk:Chord (geometry)
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I don't think this should be merged into secant line; this concept and in particular this word are far too prevalent and often used in different contexts. The proposition about "power of a point" does not fit into the secant line article. Michael Hardy 19:40, 7 November 2005 (UTC)
I second this disagree. A chord is always related to a circle, whereas a secant line is not. Also, "chord" in this context was an early trigonometric function, first tabulated by Hipparchus. Once there's a history section on this page, I think the differences should become clear. --Dantheox 20:32, 23 December 2005 (UTC)
I'm going to go ahead an remove the merge banner, as nobody has supported this merge on either page, and the additions I've made to this page make it a pretty transparently bad idea. --Dantheox 06:02, 24 December 2005 (UTC)
Another point, should the trigonometric stuff be in a separate article, possibly Chord (trigonometry)? The two are obviously related, but I'm not sure if the relationship is strong enough to put the two concepts (geometry and trig) on the same page. --Dantheox 06:09, 24 December 2005 (UTC)
[edit] Formula
I have a different issue than the underlying paragraphs. is there a formula that can tell the length of a chord? for you given information you know that the chord's endpoints are endpoints of an arc, you know the length and measure of the arc (the measure of the arc is not necassarily 90° and not necessarily 45°) as well of the radius of the circle. Is there a formula to tell me the length of this chord? If so, what is it? —The preceding unsigned comment was added by 24.187.129.93 (talk) 19:09, 26 April 2007 (UTC).
If the angle is θ, and the radius is r, then the chord if r*crdθ. (crd=2sin). The area cordoned off by the chord is (take the pie piece minus the triangle):
24.208.253.57 00:22, 11 October 2007 (UTC)
[edit] Trig One
The chord version of the trig one rule is wrong, when i put it into calculators it gives 4 not 1 —Preceding unsigned comment added by 217.208.246.94 (talk) 13:17, 28 March 2008 (UTC)
Crd x = 2*Sin(x/2)
that means Sin x = 1/2 * Crd 2x
and since Sin(90°-x)=Cos x
that means Cos x = 1/2 * Crd(2*(90°-x)) = 1/2 * Crd(180°-x)
trigometric one says
Sin² x + Cos² x = 1
if we replaces with the chords we get
(1/2 * Crd 2x)² + (1/2 * Crd(180°-2x))² = 1
simplyfy:
Crd²(2x) / 4 + Crd²(180°-2x) / 4 = 1
multiplying with 4 we get
Crd²(2x) + Crd²(180°-2x) = 4
since X doesnt matter we get
Crd²(x) + Crd²(180°-x) = 4
which also can simply be proven by putting x = 0 or 180°, one of them is going to equal 2 then, and 2 squared = 4 hence it can not again be 1
it is NOT 1 proven
—Preceding unsigned comment added by 217.208.246.94 (talk) 13:17, 4 April 2008 (UTC)
