Math/Trigonometry Question

[LaggyLou]

I am trying to figure out the length of an arc of a circle. I do not know the radius of the circle. I know the length of the chord that has the endpoints of the arc as its endpoints, and I also know the distance from the cord to the apex of the arc.

Intuitively I bvelieve I have enough information to get the length of the arc, but I am just at a loss [img]/images/graemlins/confused.gif[/img]. Van anyone help?

[PokerFink]

I'm thinking multiply the length of the cord by pi and then divide by 2?

[Evan]

This is wrong.

[mostsmooth]

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This is wrong.

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its not wrong if the chord goes through the center [img]/images/graemlins/cool.gif[/img]

[jason_t]

[ QUOTE ]
I'm thinking multiply the length of the cord by pi and then divide by 2?

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This can't be correct as it doesn't use information about the distance of the chord to the apex of the arc. That is obviously important information.

[Evan]

R= (((A/2)^2) + (B^2)) / 2B
(R = radius) (A = Chord Length) (B = Arc Height)

Angle in Radians = 2 * Arcsin((Chord Length) / (2 * Arc Radius))

Arc Length = Arc Radius * Angle in Radians

[LaggyLou]

Thanks!!!!!!! OOT Rules, and I have now achieved the feat of billing my time for posting on 2+2!

Evan, if we ever meet, the drinks are on me!

[Evan]

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Evan, if we ever meet, the drinks are on me!

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[img]/images/graemlins/grin.gif[/img]

[TBag]

Yargh, friggin trig. Hated that class. Anyways, could you explain to me why you divided by 2B when solving for the radius?

Isn't it just pythagorean's?

[Evan]

If you read my post where I said that divding by 2B was an error, forget that. It is correct. I just suck at checking simple math (I also suck at mixing up radius and diameter [img]/images/graemlins/shocked.gif[/img]). The correct formula is the one in my first post.