New kid on the Block

Joined: 10 Nov 2009
Post: 13
31 Jan 2011 12:51:23 IST
0 People liked this
2039 View Post
inmo 2011
Engineering Entrance , JEE Main , JEE Main & Advanced , Mathematics , Algebra

 i am from 10 std. i got 35 marks in rmo and was selected for inmo on 6th feb should i prepare?

Comments (5)

Cool goIITian

Joined: 25 Sep 2010
Posts: 85
31 Jan 2011 13:34:04 IST
0 people liked this

nice man.

New kid on the Block

Joined: 10 Nov 2009
Posts: 13
31 Jan 2011 14:44:51 IST
0 people liked this

 good question

can be done by extending the side AC (b) to D such that ad=ab and by similarity in triangles ABC and BDC,we get AC/BC=BC/DC.thus a/b=b+c/a and a^2=b(b+c)

I have seen it somewhere before.Maybe an old rmo question?

Hari Shankar's Avatar

Forum Expert
Joined: 28 Feb 2007
Posts: 2217
31 Jan 2011 15:13:43 IST
0 people liked this

 Congratulations Vichar!


Well as you have very little time left, I would suggest visiting


This is an international forum is most used by students preparing for math olympiads across the world


There is a large bank of questions from contests across the world over several years which you will find very useful




The angles A,B,C of the triangle are 




So the questions wants us to prove that 


But this is true as 



Blazing goIITian

Joined: 16 Jan 2010
Posts: 318
31 Jan 2011 19:08:19 IST
0 people liked this

one question for your preparation,In a triangle ABC, angle A is twice angle B. Show thata^2 = b · (b + c).

Can i try it? -> thanks

The question can be represented in the figure above....!!

We join vertex A with a point D on BC such that AD becomes the angle bisector of BAC

Now, by angle bisector theorem

c/b = m/n

=> c/b + 1 = m/n + 1

=> (b + c)/b = (m + n)/n

=> (b + c)/b = a/n ------- (i)

One more thing can be noted is

triangle ABD is isocelous

=> AD = BD = m

Again, LADC = x + x = 2x 

or, LADC = 2x

So we see triangle ABC and DAC are similar (By AAA - criterion)

=> AB/AD = BC/AC = AC/CD

=> c/m = a/b = b/n

or, a/b = b/n

=> n = b2/a

putting, the value of n in (i) we get,

(b + c)/b = a/b2/a

=> a2 = b.(b + c) proved..!!

Well if it was a question from RMO (then this is the first time that i could solve one on my own ha ha...!!)


Blazing goIITian

Joined: 16 Jan 2010
Posts: 318
31 Jan 2011 19:17:15 IST
0 people liked this

@Prophet sir-> Dear sir, i am a great fan of yours, please tell me how can i be excellent at Maths... Generally i do little errors in my maths examination, how to concentrate, focus and solve it wonderfully as you do?

Quick Reply


Some HTML allowed.
Keep your comments above the belt or risk having them deleted.
Signup for a avatar to have your pictures show up by your comment
If Members see a thread that violates the Posting Rules, bring it to the attention of the Moderator Team
Free Sign Up!
Sponsored Ads

Preparing for JEE?

Kickstart your preparation with new improved study material - Books & Online Test Series for JEE 2014/ 2015

@ INR 5,443/-

For Quick Info






Vertical Limit

Top Contributors
All Time This Month Last Week
1. Bipin Dubey
Altitude - 16545 m
Post - 7958
2. Himanshu
Altitude - 10925 m
Post - 3836
3. Hari Shankar
Altitude - 10085 m
Post - 2217
4. edison
Altitude - 10825 m
Post - 7804
5. Sagar Saxena
Altitude - 8635 m
Post - 8064
6. Yagyadutt Mishr..
Altitude - 6330 m
Post - 1958

Find Posts by Topics






Parents Corner


Fun Zone