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# Maths - Circle Theorems

Maths and statistics discussion, revision, exam and homework help.

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1. Maths - Circle Theorems
Hello,
I have my exam tomorrow and was stuck on these questions:

1) Calculate the length of AB.
I tried working out the area of a trapezium somehow but didn't get anywhere

2) A bridge is built in the shape of the arc of a circle, centre O. The width, AB, is 12m and the height is 4m. Calculate the distance AO.
I tried working out the arc length (didn't know what else to do) and was completely confused from there.

EDIT: Now finished my exam, thanks for your help everyone xx
Last edited by SM!; 13-06-2012 at 16:15.
2. 1) the distance between the two centres is 11, and you can form a right angled triangle (3 from the 7, the line between the two centres and from the centre of the smaller circle to 3 down from the other centre), then 11 x sin(3/11) ?

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3. Re: Maths - Circle Theorems
You need to be thinking about Pythagoras theorem. Make your unknown x and just work it out.
4. (Original post by acomber)
You need to be thinking about Pythagoras theorem. Make your unknown x and just work it out.
The square root of 11^2 - 3^2 is 10.6 to 1 dp.

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5. Re: Maths - Circle Theorems
(Original post by mattparker)
The square root of 11^2 - 3^2 is 10.6 to 1 dp.

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Yes.

you know the distance between the centres of the circles is 7+4=11

Call the height of the triangle 7-4 = 3cm

the unknown is then the other side, x

x = 10.583
6. Are you sure about the answer to the second one. I keep ending with 8.48(to 2 decimal place)

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7. Re: Maths - Circle Theorems
(Original post by zohaib029)
Are you sure about the answer to the second one. I keep ending with 8.48(to 2 decimal place)

Samsung > Apple
I make it 6.5.

8. Re: Maths - Circle Theorems
(Original post by zohaib029)
Are you sure about the answer to the second one. I keep ending with 8.48(to 2 decimal place)

Samsung > Apple
(Original post by mattparker)
The square root of 11^2 - 3^2 is 10.6 to 1 dp.

This was posted from The Student Room's iPhone/iPad App

(Original post by acomber)
Yes.

you know the distance between the centres of the circles is 7+4=11

Call the height of the triangle 7-4 = 3cm

the unknown is then the other side, x

x = 10.583

(Original post by notnek)
I make it 6.5.

Thank you everyone for your help xx
9. Re: Maths - Circle Theorems
(Original post by SM!)
Thank you everyone for your help xx
I assume you managed to do the second one then?

Good luck for the exam tomorrow - I'm sure you'll do well.
10. If you split line ab equally with a line from the centre you make two triangles right. Now let look at triangle aoc (were c is the perpendicular bisector from point o) i did some calculations and ended up with 8 . Im most likely wrong so could you go through your steps please and thank you

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11. Re: Maths - Circle Theorems
(Original post by zohaib029)
If you split line ab equally with a line from the centre you make two triangles right. Now let look at triangle aoc (were c is the perpendicular bisector from point o) i did some calculations and ended up with 8 . Im most likely wrong so could you go through your steps please and thank you

Samsung > Apple
You've got the right idea but you haven't posted your working so I don't know where you've gone wrong.

The key step is to notice that OC=r-4 where r is the radius of the circle. Also, AO=r. So you have a right-angled triangle AOC with lengths 6, r-4 and r so you can use Pythagoras to find r.
12. I know were Im wrong . I made an assumption which isn't true. But im stumped.help me out please

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13. Oh... Thank you very much

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14. Re: Maths - Circle Theorems
(Original post by zohaib029)
I know were Im wrong . I made an assumption which isn't true. But im stumped.help me out please

Samsung > Apple
Do you understand my last post? Can you see why OC=r-4 ?

So you have a right-angled triangle where the hypotenuse is r and the other two sides are 6 and r-4.

Use Pythagoras to write down an equation and post it here.
15. Sorry .you dint read my post before. Thanks again any way. Also if you don't mind me asking how old are you. Surely you do a level maths or summing

Samsung > Apple
16. Re: Maths - Circle Theorems
(Original post by zohaib029)
Sorry .you dint read my post before. Thanks again any way. Also if you don't mind me asking how old are you. Surely you do a level maths or summing

Samsung > Apple
I'm a maths teacher.
17. Oh ok i was starting to worry as i thought that if another Gcse student could do that and i couldnt i wasn't as good as i thought( at the moment I've got 119 /120 ums in paper one and 116/120 in paper 2)

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Last edited by zohaib029; 13-06-2012 at 18:00.

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Last updated: June 13, 2012
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