Math Is Fun Forum

Beverrrn

Member

Registered: 2015-03-09

Posts: 6

C2 Questions!

1) The diagram above shows the sector AOB of a circle with centre O and radius 6.5cm and <AOB= 0.8 radians

a) Show that the length of the chord AB is 5.06cm, to 3sf
b) The segment R, shaded in the diagram above, is enclosed by the arc AB and the straight line AB. Calculate, in cm, the perimeter of R.

Please help...

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: C2 Questions!

Hi;

What diagram?

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In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

Beverrrn

Member

Registered: 2015-03-09

Posts: 6

Re: C2 Questions!

I'm not sure how to put pictures on here, but I described it above. It's a circle, with a triangle in. O is the centre. A is one corner, B is another corner. AO and BO are both the same length (radius)

Bob

Administrator

Registered: 2010-06-20

Posts: 10,643

Re: C2 Questions!

hi Beverrrn

Welcome to the forum.

Give me a moment and I'll make a diagram (and hopefully provide a hint ... should be able to as I was once a marker for c2  )

Bob

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Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob

Bob

Administrator

Registered: 2010-06-20

Posts: 10,643

Re: C2 Questions!

How's this ?

Bob

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Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob

Bob

Administrator

Registered: 2010-06-20

Posts: 10,643

Re: C2 Questions!

if so then:

AOB is isosceles so I’ve split it along its line of symmetry.  You can halve the angle AOB, and use trig to get half the chord length.

The length of arc AOB is (angle / (2pi)) x 2 pi R  = angle x R  Then add the length of AB.

Bob

---

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob

Beverrrn

Member

Registered: 2015-03-09

Posts: 6

Re: C2 Questions!

That's a perfect diagram!
And thank you for the first part, seems so simple once you get the method aha

But for part b, why would you use length of sector? Would it not be length of arc?

Bob

Administrator

Registered: 2010-06-20

Posts: 10,643

Re: C2 Questions!

You're right.  I spotted that and have edited it now.

Got side-tracked into calculating areas.  First rule of exams: READ THE QUESTION! Whoops! 

Bob

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Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob

Beverrrn

Member

Registered: 2015-03-09

Posts: 6

Re: C2 Questions!

So for b did you get 10.26 8-)

Bob

Administrator

Registered: 2010-06-20

Posts: 10,643

Re: C2 Questions!

Oh.  You actually want me to work it out. 

Ok, then.

Yes I get 10.26

Extra suggestion.  They tell you AB so if you cannot work that out you are allowed to do part b and at least get the marks for that.

Bob

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Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob