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Geometry Difficulty 5.1 AIME, harder Find the answer

Let ω1\omega_{1} be a circle of radius 5, and let ω2\omega_{2} be a circle of radius 2 whose center lies on ω1\omega_{1}. Let the two circles intersect at AA and BB, and let the tangents to ω2\omega_{2} at AA and BB intersect at PP. If the area of ABP\triangle ABP can be expressed as abc\frac{a \sqrt{b}}{c}, where bb is square-free and a,ca, c are relatively prime positive integers, compute 100a+10b+c100a+10b+c.

A number or a short expression. Spacing and $ signs are ignored.

Solution

Let O1O_{1} and O2O_{2} be the centers of ω1\omega_{1} and ω2\omega_{2}, respectively. Because O2AP+O2BP=90+90=180\angle O_{2}AP+\angle O_{2}BP=90^{\circ}+90^{\circ}=180^{\circ} quadrilateral O2APBO_{2}APB is cyclic. But O2,AO_{2}, A, and BB lie on ω1\omega_{1}, so PP lies on ω1\omega_{1} and O2PO_{2}P is a diameter of ω1\omega_{1}. From the Pythagorean theorem on triangle PAP2PAP_{2}, we can calculate AP=46AP=4\sqrt{6}, so sinAOP=265\sin \angle AOP=\frac{2\sqrt{6}}{5} and cosAOP=15\cos \angle AOP=\frac{1}{5}. Because AOP\triangle AOP and BOP\triangle BOP are congruent, we have sinAPB=sin2AOP=2sinAOPcosAOP=4625\sin \angle APB=\sin 2 \angle AOP=2 \sin \angle AOP \cos \angle AOP=\frac{4\sqrt{6}}{25} implying that [APB]=PAPB2sinAPB=192625[APB]=\frac{PA \cdot PB}{2} \sin \angle APB=\frac{192\sqrt{6}}{25}

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