Arhhh!! I struggle with circle geometry!! (1 Viewer)

Gussy Booo

Mathematics <3
Joined
Aug 1, 2009
Messages
251
Location
Sydney
Gender
Male
HSC
2010
Especially proving things ! I do not know where to start!

Can anyone who's really good at this topic give me some hints.

I've done a lot of study, I'm memorized theorems and stuff, but I'm lacking process.

Can anyone give me a good and understandable process in solving Circle Geo questions.

I took to account to memorize my congruency and similarity properties again.

Gosh ! Arh! CIRCLESSSSSSSSSSSSSSSSSSS
 

Rockyroad

Banned
Joined
Jun 16, 2008
Messages
461
Location
The Gong.
Gender
Female
HSC
2009
Aww but it's so fun.
Trig needs to go die. But circle geometry is heaps fun.
I guess just know your thereoms really well and get teacher's help to go through it slowly.
 

Drongoski

Well-Known Member
Joined
Feb 22, 2009
Messages
4,255
Gender
Male
HSC
N/A
Especially proving things ! I do not know where to start!

Can anyone who's really good at this topic give me some hints.

I've done a lot of study, I'm memorized theorems and stuff, but I'm lacking process.

Can anyone give me a good and understandable process in solving Circle Geo questions.

I took to account to memorize my congruency and similarity properties again.

Gosh ! Arh! CIRCLESSSSSSSSSSSSSSSSSSS

Post a couple of questions u've had problems with and indicate what these are so we can try to identify the sources/causes of yr difficulties. Asking a very general question will only elicit general and sometimes not very useful advice.
 
Last edited:

cutemouse

Account Closed
Joined
Apr 23, 2007
Messages
2,250
Gender
Undisclosed
HSC
N/A
Just do lots of questions... seriously. I actually got the circle geometry question in my trials. And I thought I sucked at it before.

A bit tricky though... It incorperated geometry too (ie. angle sum of a quadrilateral is 360 deg).
 

gcchick

Come at me bro
Joined
Sep 7, 2007
Messages
765
Location
Brisvegas
Gender
Female
HSC
2008
Uni Grad
2015
Just do lots of questions... seriously. I actually got the circle geometry question in my trials. And I thought I sucked at it before.

A bit tricky though... It incorperated geometry too (ie. angle sum of a quadrilateral is 360 deg).
This. I absolutely HATED circle geometry to start off with because I couldn't seem to grasp the concepts. I did a heap of questions each week and it ended up being one of the easiest topics to me. So practice, practice, practice.
 

lychnobity

Active Member
Joined
Mar 9, 2008
Messages
1,292
Gender
Undisclosed
HSC
2009
Post a couple of questions u've had problems and indicate where u're having problems so we can try to identify the source/cause of yr difficulties. Asking a very general question will only elicit general and sometimes not very useful advice.
+1
Honestly Drongoski, you are the most rep worthy member. Why can I not rep you again?!

But I'll try:
Sure, remembering all the theorems will only go so far. You have to learn to INTERPRET what the question is asking. In the HSC, they'll usually have some follow up questions, which will give you ideas on how to proceed to the final hardest part.

______________________
FOR EXAMPLE

NB: I'm making this up, so it's a dodgy question

Prove that AB.EC = BC.DE (look at the diagram in next post)

You have no information about the sides at all. None of the rules fit the theorems. All the stuff on the diagram relates to angles. The only tool you have left that allows you to prove the sides are in the same ratio, is similar triangles.

Since the question asks about the sides, you have to choose the triangles that contain them. ie triangles ABC and DEC

To prove similar triangles, you find whether they fulfil one of the following:
1) Equiangular
2) Sides in same ratio
3) 2 sides in the same ratio about an equal angle

The question provides no information about sides, so you must use the equiangular proof.

In triangle ABC and DEC:
angle ACB is common

As hard as you look, you won't find a theorem that allows any of the other angles in ABC to equal any of the other angles in DEC. So, the only other option is finding a third angle.

And... you do the rest.

The solution will show up when you put your mouse over the box.

angle PCA = angleBAC (alt angles)
angle PCA = angleDEC (chord to tangent's poc = angle in alt segment)

.'. angleBAC = angleDEC

In triangle ABC and DEC:
angle ACB is common
angle BAC = angle DEC (proved above)
angle ABC = angle EDC (3rd angle)
.'. triangle ABC and DEC are similar

Since angle BAC = angle DEC, AB/BC = DE/EC (ratio of sides in similar triangles)

Rearrange it, AB.EC = BC.DE
 
Last edited:

_GOD_

Member
Joined
Aug 5, 2009
Messages
36
Gender
Male
HSC
2009
Practice and Practice, then after that Practice
 

Gussy Booo

Mathematics <3
Joined
Aug 1, 2009
Messages
251
Location
Sydney
Gender
Male
HSC
2010
AHHHHHHHHHHHHHHHHHHHHHHHHHHHH !!!!!!!

ITS SOO CLEAR WHEN YOU SEE THE SOLUTION!!

DAMMITTT! I HAVE TO KEEP PRACTISING!!!

This is soo imbarising for me ! Why can't I get this ! Arh! I won't stop!!

I couldn't see the small alternate segment.

The problem with me is, whenever I see a pathway to a solution, I keep continuing and wondering how to do it. Rather then STOP and say, maybe there's another way.

E.g I took the larger Alternate Segment instead of the smaller one.

TYVM mate. I will keep practising.
 

lychnobity

Active Member
Joined
Mar 9, 2008
Messages
1,292
Gender
Undisclosed
HSC
2009
E.g I took the larger Alternate Segment instead of the smaller one.
You can only take the larger alternate segment iff PL was a tangent to the larger circle.

"The angle formed between a tangent and chord drawn to a tangent's point of contact equals the angle in the alternate segment"
 

Gussy Booo

Mathematics <3
Joined
Aug 1, 2009
Messages
251
Location
Sydney
Gender
Male
HSC
2010
AHHH!!!!!!!!!!!!!!!!!!!!!!!!!
Again! DAMMIT!! WHY CANT I SEE THESE THINGS!!!
Lmfao ! yes dammit! Omgsshhh!!!!!
Tyvm. Im getting of BoS. Im going to do as many questions as i can. Till death
 

killua_3

Member
Joined
Mar 21, 2009
Messages
51
Location
Away from you
Gender
Male
HSC
2009
i find that the best way to deal with circle geometry is to work backwards. what i mean by this is that when you see the question, you have to think to your self what rule will prove this. knowing what properties must prove makes it a lot easier imo. you can try turning the page around, just to give you another perspective on the problem, you never know, it may help.

also, if you are using more than 2 angles then (generally) that means you are making it too complicated.
 

Gussy Booo

Mathematics <3
Joined
Aug 1, 2009
Messages
251
Location
Sydney
Gender
Male
HSC
2010
5 hours later !! 1000xx better at circle geometry !! Omgshhh !!!
Practice is something you cant buy!

I'm finally getting the hang of proving. However, correct me if I'm wrong, there are plenty of ways of proving questions right?

Thanks for your help guys :) , and yes, working backwards is pretty coool.

I'm going to do some practice exams now. !
 

Timothy.Siu

Prophet 9
Joined
Aug 6, 2008
Messages
3,449
Location
Sydney
Gender
Male
HSC
2009
yep, theres sometimes more than one way of doing a question, especially if theres lots of lines and stuff.
 

Gussy Booo

Mathematics <3
Joined
Aug 1, 2009
Messages
251
Location
Sydney
Gender
Male
HSC
2010
Ahh!! I just sat my Maths ext exam. Period 5 Friday! Woooo!

I did...well....it feels weird. Because I got 100% in my 2unit exam, I've kinda put myself in high expectations, so arhhh i'm a bit .....anxious you could say.

I'm pretty happy, caught this Trisection question out..however..I LEFT 4 MARKSS !! DAMMIT!!
FOUR BLOODY MARKSS !!!!!!!!!!!!!!!!!!!!!!!!!!!!
..

... wait for it...


on Circle Geometry !!! Dammit, I could'nt prove this Cyclic Quad!!! I'm so weak with Cyclics! Everything else went pretty sweeeet ! Im hoping for a 85%...or 80% sigh................!!
 

lpodnano

5eva alone
Joined
Mar 6, 2008
Messages
1,561
Location
;)
Gender
Female
HSC
2011
Circle geometry is actually my favourite this year. Trigonometry is also alright. It took me a while to grasp the concept of it but after that it was just like any other math subject.
 

ninetypercent

ninety ninety ninety
Joined
May 23, 2009
Messages
2,148
Location
Sydney
Gender
Female
HSC
2010
Circle Geometry is hard :( it's harder than Probability, but perhaps equal to Permutations :p
 

Users Who Are Viewing This Thread (Users: 0, Guests: 1)

Top