1 vector AB? BC>0, that is, c * a * cos (π-b) > 0, ∴ b > π/2, △ABC is an obtuse triangle;

② If COSA * TANB * COSC

③ If Sinasinb

④ if acosA=bcosB, ∴ acosA=a(sinB/sinA)*cosB, it is simplified as sin2A=sin2B, and △ABC is an isosceles triangle;

The question given is correct;