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Subject: Math , asked on 9/2/11

# IF FROM ANY POINT ON THE COMMON CHORD OF TWO INTERSECTING CIRCLES,TANGENTS BE DRAWN TO THE CIRCLES PROVE THAT THEY ARE CONGRUENT.....Ref.10th R.D. Sharma cbse mathematics book, lesson 11(circles), exercise 11.2 question no.3plz ans..

Hi Cheral!

In order to prove your question we will use one property. It can be stated as Let PT be a tangent to the circle from an exterior point P and a secant to the circle through P intersects the circle at points A and B where T is a point on the circle, then PT2 = PA.PB. First of all I will prove this and use it to prove your question.

Let PT be a tangent to the circle from an exterior point P and a secant to the circle through P intersects the circle at points A and B where T is a point on the circle

Using Pythagoras theorem for ∆OPT
OT2 + PT2 = OP2
r 2 + PT2 = r 2 + PA.PB  [using (2)]
⇒PT2 = PA.PB    … (3)
Now, I will use this result to prove your question.
The information provided by you is represented diagrammatically as
Here, the circles intersect at point X and Y. A is a point on the line joining the points X and Y. AM and AN are the tangents drawn to the circles
You need to prove AM = AN
Using (3), it can be said that
AM2 = AX.AY and AN2 = AX.AY
Thus, AM2 = AN2
⇒AM = AN
Hence, proved

Cheers!

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• 1

thank u sir........  i posted this question many times but none of the students could answer it correctly............. either they were confused or regarded it as a wrong ques. or used AXY as a tangent........... once again thank u very much sir........

• -1

thank u sir........  i posted this question many times but none of the students could answer it correctly............. either they were confused or regarded it as a wrong ques. or used AXY as a tangent........... once again thank u very much sir........

• -1

repeated posting wont yield answer!! :D

• -1

thumbs up from me..............