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Olympiad workbook
Exam
Olympiad workbook
Subject
IOQM
Chapter
Circle

Olympiad workbook · IOQM · Circle

Two circles, S_1 and S_2 , of radii 6 units and 3 units...

Two circles, S1S_1 and S2S_2, of radii 6 units and 3 units respectively, are tangent to each other externally. Let ACA C and BDB D be their direct common tangents with AA and BB on S1S_1, and CC and DD on S2S_2. Find the area of quadrilateral ABDCA B D C to the nearest integer.Two circles, S_1 and S_2 , of radii 6 units and 3 units respectively, are tangent to each other externally. Let A C and

Correct answer

68

Step-by-step solution

Refer to diagram, Two circles, S_1 and S_2 , of radii 6 units and 3 units respectively, are tangent to each other externally. Let A C and
cos⁡θ=39=13\cos \theta=\frac{3}{9}=\frac{1}{3} Let ar⁡(△APR)=Δ\operatorname{ar}(\triangle A P R)=\Delta then ar⁡(△BQS)=Δ4\operatorname{ar}(\triangle B Q S)=\frac{\Delta}{4} Because △APR∼△BQS\triangle A P R \sim \triangle B Q S Δ=12AP⋅PRsin⁡θ=126⋅2⋅223=42\begin{aligned} \Delta & =\frac{1}{2} A P \cdot P R \sin \theta \\ & =\frac{1}{2} 6 \cdot 2 \cdot \frac{2 \sqrt{2}}{3}=4 \sqrt{2} \end{aligned} Area of □ABDC=2\square A B D C=2\left[\frac{1}{2} \sqrt{72}(3+6)-\Delta+\frac{\Delta}{4}\right] =48 \sqrt{2}
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