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## #1 2013-02-26 03:14:23

shivusuja
Member
Registered: 2006-09-14
Posts: 56

### Geometry

Two circles intersect at P & Q. Through P , two straight lines APB & CPD are drawn to meet the circles at A , B, C,& D. AC & DB when produced meet at O. Show that OAQB is cyclic quadrilateral

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## #2 2013-02-26 12:50:58

bob bundy
Registered: 2010-06-20
Posts: 8,108

### Re: Geometry

Hi

Maybe joining PQ and playing around with equal angles made by same chord will work.

I will come back to this when I am able.

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

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## #3 2013-02-26 13:07:39

bob bundy
Registered: 2010-06-20
Posts: 8,108

### Re: Geometry

Like this

A C D = A Q P

O D C = P Q B

So A O B add A Q B = 180

Hope you can fill the gaps

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

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## #4 2013-02-28 07:54:56

bob bundy
Registered: 2010-06-20
Posts: 8,108

### Re: Geometry

Since Yesterday Iam Strugling With That. Does The Point O Comes Out Of The Circles. How Is ACD= AQB.
Iam Find ACD+AQB=180.  Please Can  You  Give More Clarity

Yes, point O is outside the circles.

ACD is not = to AQB.

I said ACD = AQP

With AP as a chord, angle ACP = angle AQP because they are two angles on the circumference made by the same chord.

ACP = ACD because C-P-D is a straight line.

Hence ACD = AQP

Then

QPDB is cyclic so PQB + PDB = 180.

But on the straight line ODB,  angle ODC + PDB = 180

therefore, angle ODC = angle PQB.

So we have in triangle OCD,

OCD + ODC + DOC = 180     =>    ACD + PQB + DOC = 180    =>     (AQP +PQB) + DOC = 180      =>   AQB + DOA = 180

So OAQB is cyclic.

Hope that clears it up.

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

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## #5 2013-02-28 16:50:40

shivusuja
Member
Registered: 2006-09-14
Posts: 56

Hi Bob
Thanks A Lot

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