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Prove that the lengths of two tangents drawn from an external point to a circle are equal.

 

 

 

 
 
 
 
 

Answers (1)

Let circle with centre O has two tangents AB and AC.

To prove \rightarrow AB=AC

Construction \rightarrow Join AO, BO and OC

Proof \rightarrow  OB \perp AB\; \; \text{and}\; \; OC\perp AC  (Tangent at any point of the circle is perpendicular to the radius)

\Rightarrow \angle OBA= \angle OCA=90^{\circ}

In \bigtriangleup ABO and  \bigtriangleup ACO

\Rightarrow \angle OBA= \angle OCA  (both 90^{\circ})

\Rightarrow OB=OC                 (radius of the circle)

\Rightarrow OA=OA                 (common)

By R.H.S congruency  \bigtriangleup ABO \cong \bigtriangleup ACO

Hence by CPCT : AB=AC

Hence proved.

 

 

Posted by

Ravindra Pindel

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