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Right triangle with uniform legs and a wide angle

Question

Build a right triangle whose two legs AA and BB have lengths drawn independently from Unif(0,1)\text{Unif}(0,1). Let θ\theta denote the acute angle lying opposite leg AA. The probability that θ>π/3\theta > \pi/3 can be written as abc\dfrac{a}{b\sqrt{c}} with a,b,ca,b,c positive integers that are relatively prime. Compute abcabc.

Short answer

66. Since tan⁡θ=A/B\tan\theta = A/B, the event is A>3 BA>\sqrt3\,B. In the unit square this is a triangle with legs 11 and 1/31/\sqrt3, of area 123\tfrac{1}{2\sqrt3}, so a=1,b=2,c=3a=1,b=2,c=3 and abc=6abc=6.

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