Thread: Circle Question

1. Circle Question

How do you do this question?

Any help would be appreciated.
Thanks!

2. Re: Circle Question

1. Find the area of the two sectors, add them together.

2. Find the area of the trapezium.

3. area of trapezium minus area of the sectors.

3. Re: Circle Question

Yea I thought of that too, but I can't find the unkown angle to find the sectors lol...
BTW can I assume that the lines drawn to A and B are perpendicular to it?

4. Re: Circle Question

Ah you cant find the angle because you are only given the radius, have to find another approach

5. Re: Circle Question

I did it in degrees since your profile says HSC 2014 ie: You don't know radians yet (but it would have made the working out nicer).

6. Re: Circle Question

Originally Posted by kazemagic
Yea I thought of that too, but I can't find the unkown angle to find the sectors lol...
BTW can I assume that the lines drawn to A and B are perpendicular to it?
yes

7. Re: Circle Question

Originally Posted by kazemagic
Yea I thought of that too, but I can't find the unkown angle to find the sectors lol...
BTW can I assume that the lines drawn to A and B are perpendicular to it?
Yes you can. When the radius touches the point of contact of the tangent, it is perpendicular to the tangent.

8. Re: Circle Question

Ah! Thanks carrotsticks so smart :O it never came across to my mind DC would be the addition of 2 radii lol

Also, thanks guys for your input

9. Re: Circle Question

Originally Posted by qwerty44
Yes you can. When the radius touches the point of contact of the tangent, it is perpendicular to the tangent.
That's 3u

10. Re: Circle Question

Originally Posted by Sanjeet
That's 3u
But the question can't be answered without that assumption, regardless of which course it is taught in.

11. Re: Circle Question

Originally Posted by qwerty44
But the question can't be answered without that assumption, regardless of which course it is taught in.
It can be done without that theorem. You just have to construct a line that meets the two radii at right angles (like carrot has done).

12. Re: Circle Question

Originally Posted by Carrotsticks
I did it in degrees since your profile says HSC 2014 ie: You don't know radians yet (but it would have made the working out nicer).

beast

13. Re: Circle Question

Originally Posted by qwerty44
But the question can't be answered without that assumption, regardless of which course it is taught in.
Carrotsticks just did...

14. Re: Circle Question

Originally Posted by Sanjeet
That's 3u
O_O i thought circle geometry is year 10 lol?

15. Re: Circle Question

Originally Posted by kazemagic
O_O i thought circle geometry is year 10 lol?
Some schools do it in year 10, but it's really only the basics iirc. You learn it in more depth in 3U.

16. Re: Circle Question

Originally Posted by kazemagic
O_O i thought circle geometry is year 10 lol?
Lol no it's in the 3u prelim course

17. Re: Circle Question

O_O that's weird I would have sworn that radii touching tangent thing theorem was in mathscape year 10 lol...

18. Re: Circle Question

Originally Posted by Sanjeet
Lol no it's in the 3u prelim course
It can be done in year 10 5.3 at the end of the course.

19. Re: Circle Question

Originally Posted by Sanjeet
Carrotsticks just did...
Oops. My mistake, sorry!

20. Re: Circle Question

Originally Posted by RealiseNothing
It can be done in year 10 5.3 at the end of the course.
Actually, a capable student in year 9 could probably do it. I recall it being in the AMC paper on intermediate level.

21. Re: Circle Question

Originally Posted by Demento1
Actually, a capable student in year 9 could probably do it. I recall it being in the AMC paper on intermediate level.
I meant, some schools do it at the end of the 5.3 course. As in, it's in the optional part of the syllabus.

But I agree, a capable student could do it a lot earlier, similar to the basics of complex numbers - they can be done in year 8 imo.

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