Have a look at this theorem:
http://www.mathisfunforum.com/viewtopic … 09#p365709
So you can write the perimeter in terms of the length of two tangents from C.
There's a formula for the radius given the sides of a triangle:
https://en.wikipedia.org/wiki/Incircle_ … gle#Radius
And cosine rule to get angle C and hence half C. Then more trig to finish off.
Bob
]]>