The diagonals AC and BD of a cyclic quadrilateral ABCD intersect each ...

Here, AC and BD are chords of the circle.
∴ AP . CP = BP . DP
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The diagonals AC and BD of a cyclic quadrilateral ABCD intersect each ...

Here, AC and BD are chords of the circle.
∴ AP . CP = BP . DP
The diagonals AC and BD of a cyclic quadrilateral ABCD intersect each ...
Explanation:
Given, ABCD is a cyclic quadrilateral. This means that all four vertices of the quadrilateral lie on a circle.
Property 1: In a cyclic quadrilateral, opposite angles are supplementary.
In quadrilateral ABCD, angle A + angle C = 180 degrees and angle B + angle D = 180 degrees.
Property 2: In a cyclic quadrilateral, opposite angles are equal.
In quadrilateral ABCD, angle A = angle C and angle B = angle D.
Property 3: The opposite sides of a cyclic quadrilateral are in the same ratio.
In quadrilateral ABCD, AB/CD = BC/DA.
Property 4: The opposite angles of a cyclic quadrilateral are in the same ratio.
In quadrilateral ABCD, angle A/angle C = angle B/angle D.
Proof:
To prove that AP.CP = BP.DP, we will use the properties of cyclic quadrilaterals.
Step 1: Extend AP and CP to meet the circumcircle of ABCD at points E and F, respectively.
(Fig 1: AP and CP extended)
Step 2: Since ABCD is a cyclic quadrilateral, angle A = angle C and angle B = angle D.
(Fig 2: Angle equality)
Step 3: In triangle APE, angle A = angle C (opposite angles of a cyclic quadrilateral).
Therefore, triangle APE is an isosceles triangle, and AE = PE.
Similarly, in triangle CPF, angle B = angle D (opposite angles of a cyclic quadrilateral).
Therefore, triangle CPF is an isosceles triangle, and CF = PF.
(Fig 3: Isosceles triangles)
Step 4: Applying property 3, we have AB/CD = BC/DA.
Dividing both sides by BC, we get AB/BC = CD/DA.
Using the property of similar triangles (APE and BPC are similar), we have AP/BP = AE/CF.
Similarly, using the property of similar triangles (CPF and DPA are similar), we have DP/CP = PF/CF.
Step 5: Combining the above two equations, we get AP/BP * DP/CP = AE/CF * PF/CF.
Simplifying further, we get AP.BP/CP.DP = AE.PF/CF.CF.
Since AE = PE and CF = PF, we have AP.BP/CP.DP = PE.PF/CF^2.
But PE.PF = PA.PB (product of lengths of tangents from a point to a circle).
Therefore, we have AP.BP/CP.DP = PA.PB/CF^2.
Step 6: In triangle CPF, angle B = angle D (opposite angles of a cyclic quadrilateral).
Therefore, triangle CPF is an isosceles triangle, and CF = PF.
Using the property of similar triangles (APE and BPC are similar), we have AP/BP = AE/CF.
Therefore, AP.BP = AE.CF.
Step 7: