Circle Question (1 Viewer)

[kazemagic]

How do you do this question?

Any help would be appreciated.
Thanks!

 

[Timske]

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.

 

[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?

 

[Timske]

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

 

[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).

 

[Timske]

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

 

[qwerty44]

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.

 

[kazemagic]

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

 

[Sanjeet]

Yes you can. When the radius touches the point of contact of the tangent, it is perpendicular to the tangent.

That's 3u

 

[qwerty44]

That's 3u

But the question can't be answered without that assumption, regardless of which course it is taught in.

 

[RealiseNothing]

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).

 

[Magical Kebab]

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

 

[Sanjeet]

But the question can't be answered without that assumption, regardless of which course it is taught in.

Carrotsticks just did...

 

[kazemagic]

That's 3u

O_O i thought circle geometry is year 10 lol?

 

[RealiseNothing]

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.

 

[Sanjeet]

O_O i thought circle geometry is year 10 lol?

Lol no it's in the 3u prelim course

 

[kazemagic]

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

 

[RealiseNothing]

Lol no it's in the 3u prelim course

It can be done in year 10 5.3 at the end of the course.

 

[qwerty44]

Carrotsticks just did...

Oops. My mistake, sorry!

 

[Demento1]

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.