1-sina^2+ 1-sinb^2+ 1-sinc^2= 1

sinA^2+sinB^2+sinC^2=2

A/sinA=b/sinB=c/sinC=2r。

Therefore: (a/2r) 2+(b/2r) 2+(c/2r) 2 = 2.

a^2+b^2+c^2=8r^2

So it is a right triangle.