All Obtained Different Results? Who's Right?

Students Michaelle, Maeve, Barbara and Antony, are asked to solve the equation $2\sin x +\cos x -1=0$. Who solved it correctly?

• Michaelle found as the solution set $\\\displaystyle S=\left \{ 2k\pi ,\,\arccos\left ( -\frac{3}{5} \right )+2k\pi \right \}$
• Maeve found $\\\displaystyle S=\left \{ 2k\pi ,\pi-\arcsin \frac{4}{5} +2k\pi \right \}$
• Barbara found $\\\displaystyle S=\left \{ 2k\pi ,2\arctan2 +2k\pi \right \}$
• Antony found $\\\displaystyle S=\left \{ 2k\pi ,\pi - 2\arcsin\frac{\sqrt{5}}{5} +2k\pi \right \}$