Can you solve without trig?

Geometry Level 4

Triangle A B C ABC inscribed a circle ( O ; 1 ) (O;1) . If A = 6 0 \angle A = 60 ^\circ and C = 4 5 \angle C = 45 ^\circ , 2 times the perimeter of the triangle can be written as a m + b n + c p a \sqrt{m} + b\sqrt{n} + c\sqrt{p} , where a , b , c , m , n , p a,b,c,m,n,p are positive integers and m , n , p m,n,p are distinct squarefrees. Find a b c + m n p abc+mnp .

Note: 'Cause I don't like trigonometry, please post solutions using only trigonometric functions of these angles: 3 0 , 4 5 , 6 0 30 ^\circ,45 ^\circ,60 ^\circ

Inspired by my math exercise.


The answer is 42.

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1 solution

Ahmad Saad
Mar 20, 2016

There's a small mistake that you've stated sin 7 5 = cos 3 0 \sin 75 ^\circ = \cos 30 ^\circ . It must be cos 1 5 \cos 15 ^\circ instead. Anyway, that's a good solution.

Tran Quoc Dat - 5 years, 2 months ago

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Thanks for your remark. I've corrected it.

Ahmad Saad - 5 years, 2 months ago

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