two tangents PA and PB are drawn to a circle with centre O from an extwrnal pount
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In triangle APB, PA = PB , So angle PAB = angle PBA .
Also angle PAO = angle PBO = 90 deg.
Hence angle OAB = angle OBA.
In the triangle AOB :angle AOB = 180 - 2*angle OAB.
In the quadrangle PABO:angle AOB = 360 - 90 - 90 - angle APB.
Hence angle APB = 2 * angle OAB.
Also angle PAO = angle PBO = 90 deg.
Hence angle OAB = angle OBA.
In the triangle AOB :angle AOB = 180 - 2*angle OAB.
In the quadrangle PABO:angle AOB = 360 - 90 - 90 - angle APB.
Hence angle APB = 2 * angle OAB.
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