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#1 2013-02-18 14:24:49

KIRA c:
Guest

Circles: Arc Length Help

I've been trying to do these for a while and just can't figure them out. I've asked my parents, but they don't know either, soI asked my teacher and they told me to just use the equation, which I have been doing, so that was no help.

Formula is:
L = (n/360)(2(PI)r)

Where:
L = Length, n = degree measure of arc, r = radius of the circle.

In these questions I need to find the arc length.

11. r=10 n=20

A) 15(pi)/ 7
B) 13(pi)/ 5
C) 16(pi)/ 2
D) 11(pi)/ 4
E) 10(pi)/ 9
F) 9(pi)/ 4

So, I set up the equation L = (20/360)(2(PI)10). Then I reduced the first part, L = (1/18)(20(PI)). So the answer would be 20(PI)/18? I'm just so lost on this.

Other Questions That are Similar That I Don't Understand:

12. r=3 n=6

A) pi/9
B) pi/12
C) pi/26
D) pi/10
E) pi/8
F) pi/4

13. r=4 n=7

A) 8(pi)/55
B) 6(pi)/12
C) 7(pi)/45
D) 2(pi)/22
E) 9(pi)/18
F) 7(pi)/37

14. r=2 n=x

A) x(pi)/15
B) x(pi)/30
C) x(pi)/60
D) x(pi)/90
E) x(pi)/120
F) x(pi)/150

Then, how would you find the radius if:

16. n=30 L=1/3xy(pi)

A) 6xy
B) 8xy
C) 2xy
D) 10xy
E) 3xy
F) 14xy

I don't know how to do this one at all.

#2 2013-02-18 15:11:21

bobbym
Administrator
From: Bumpkinland
Registered: 2009-04-12
Posts: 86,776

Re: Circles: Arc Length Help

Hi;

So, I set up the equation L = (20/360)(2(PI)10). Then I reduced the first part, L = (1/18)(20(PI)). So the answer would be 20(PI)/18? I'm just so lost on this.

Try reducing 20 / 18. Then it will look like answer E.

12) I have D.

13) C

14) D

For 16, do you mean?

Last edited by bobbym (2013-02-18 19:48:57)


In mathematics, you don't understand things. You just get used to them.
Of course that result can be rigorously obtained, but who cares?
Combinatorics is Algebra and Algebra is Combinatorics.

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#3 2013-02-21 07:48:01

KIRA c:
Guest

Re: Circles: Arc Length Help

I submitted it and got a 19/20! Thanks everyone!

#4 2013-02-21 10:18:16

bobbym
Administrator
From: Bumpkinland
Registered: 2009-04-12
Posts: 86,776

Re: Circles: Arc Length Help

Hi;

Congratulations, that is a nice score.


In mathematics, you don't understand things. You just get used to them.
Of course that result can be rigorously obtained, but who cares?
Combinatorics is Algebra and Algebra is Combinatorics.

Offline

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