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In the figure (ii) given below, the diagonals of a cyclic quadrilateral ABCD intersect in P and the area of the triangle APB is 24 cm2. If AB = 8 cm and CD = 5 cm, calculate the area of △DPC.

In the figure (i) given below, PR is a diameter of the circle, PQ = 7 cm, QR = 6 cm and RS = 2 cm. Calculate the perimeter of the cyclic quadrilateral PQRS. Circles, ML Aggarwal Understanding Mathematics Solutions ICSE Class 10.

Circles

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Answer

In △ABP and △DPC,

∠APB = ∠DPC (∵ vertically opposite angles are equal.)

∠ABP = ∠DCP (∵ angles in same segment are equal.)

△APB ~ △DPC. (By AA axiom)

We know that ratio of the area of similar triangles is the ratio of their corresponding sides.

Area of △APBArea of △DPC=AB2CD224Area of △DPC=6425Area of △DPC=24×2564Area of △DPC=60064Area of △DPC=758Area of △DPC=938.\therefore \dfrac{\text{Area of △APB}}{\text{Area of △DPC}} = \dfrac{AB^2}{CD^2} \\[1em] \Rightarrow \dfrac{24}{\text{Area of △DPC}} = \dfrac{64}{25} \\[1em] \Rightarrow \text{Area of △DPC} = \dfrac{24 \times 25}{64} \\[1em] \Rightarrow \text{Area of △DPC} = \dfrac{600}{64} \\[1em] \Rightarrow \text{Area of △DPC} = \dfrac{75}{8} \\[1em] \Rightarrow \text{Area of △DPC} = 9\dfrac{3}{8}. \\[1em]

Hence, the area of △DPC = 9389\dfrac{3}{8} cm2.

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