1.

From a point P two tangents are drawn to a circle with center o. if OP = diameter of the circle, show `triangleAPB` is equilateral.

Answer» In `triangle OAP`
OP=2r
`Sintheta=(OA)/(OP)=r/(2r)=1/2`
`sin theta=30^0`
`angleOPA=30^o`
similarly,
`angleOPB=30^o`
`angleAPB=angleOPA+angleOPB`
`=30^o+30^o`
`=60^o`
In`trianglePAB`
`anglePAB=anglePBA`
`anglePAB+anglePBA+angleAPB=180^o`
`2anglePAB=120^o`
`angle PAB=60^o`
so, `anglePBA=60^o`
and`angleAPB=60^o`
so, `triangleAPB` is an equilateral triangle


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