Nếu tan \(\dfrac{\beta}{2}\) = 3 tan\(\dfrac{\alpha}{2}\) thì tan \(\dfrac{\alpha+\beta}{2}\) tính theo α bằng
A. \(\dfrac{2cos\alpha}{2sin\alpha-1}\)
B. \(\dfrac{2sin\alpha}{2cos\alpha-1}\)
C. \(\dfrac{2cos\alpha}{2sin\alpha+1}\)
D. \(\dfrac{2sin\alpha}{2sin\alpha-1}\)