Thursday, 8 September 2016

geometry - Easier way of finding radius of circle inscribed in a scalene triangle given 2 sides and the included angle

I have a scalene triangle with two sides given and the included angle. I am solving for the radius of the inscribed circle. See the image below.
enter image description here



I know that I can use the law of Cosines to find the length of the missing side
$c^2=a^2+b^2-2ab cosC$




Then I could use area of a triangle formula



$K=\frac12absin C$



Finally I could find and insert the perimeter and area into the formula below to solve for r.



$r=\frac{2A}p$



My equation for r would be:




$r=\frac{ab \sin{C}}{a+b+\sqrt{a^2+b^2-2ab \cos{C}}}$



Using the given data this would give me:



$r=\frac{119*202*sin(43)}{119+202+\sqrt{119^2+202^2-2*119*202*cos(43)}}=35.5$



Is there a simpler way to do this?

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