to Prove: A line drawn perpendicular from P will pass from O.
Given: APB is tangent to circle with centre O.
Let us consider a circle with centre O. Let AB be a tangent which touches the circle at P.
Assume that the perpendicular to AB at P does not pass through centre O. Let it pass through another point O'. Join OP and O'P.
As perpendicular to AB at P passes through O', therefore,
∠ O'PB = 90° ... (1)
O is the centre of the circle and P is the point of contact.
We know the line joining the centre and the point of contact to the tangent of the circle are perpendicular to each other.
∴ ∠ OPB = 90° ... (2)
Comparing equations (1) and (2), we obtain
∠ O'PB = ∠ OPB ... (3)
From the figure, it can be observed that,
∠ O'PB < ∠ OPB ... (4)
Therefore, ∠ O'PB = ∠ OPB is not possible. It is only possible, when the line O'P coincides with OP.
Therefore, the perpendicular to AB through P passes through centre O.
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