From A/COSA = B/COSB, we get A/B = COSA/COSB.

And a/Sina = b/sinb, ∴ a/b = Sina/sinb.

∴sinA/sinB=cosA/cosB。

∴sinAcosB=cosAsinB，

Sin(A-B)=0, A = B. Similarly, B = C.

△ ABC is an equilateral triangle.