Multiply the above two formulas:
(cosA*sinA )/(cosBsinB)= 1
cosA*sinA =cosBsinB
Sin2a = sin2B and 2B are both greater than 0.
2A=2B or 2A=π-2B
So A=B or A+B=π/2.
Triangle ABC is an isosceles triangle (A=B) or a right triangle (C=π/2).