The radius of the inscribed circle r=c/2.
2. Triangle area S = ABS Inc/2 = (A 2+B 2-C 2)/4.
sinC=(a^2+b^2-c^2)/2ab=cosC
tanC= 1
C=45 .
3.4=AB*BC*sinC/2
sinC=4/5
CosC=3/5 or -3/5.
4.a+b=3,∠C=60
c/sinC=2
C=2sinC= root number 3
cosC=(a^2+b^2-3)/2ab= 1/2
a^2+b^2=ab+3
a+b=3
(a+b)^2=3ab+3=9
ab=2
S=absinC/2= root number 3/2.