$\alpha=60^\circ$\alpha=60^\circ

$\alpha\in\left(40^\circ ,60^\circ \right)$\alpha\in\left(40^\circ ,60^\circ \right)

$\alpha\in\left(30^\circ ,40^\circ \right)$\alpha\in\left(30^\circ ,40^\circ \right)

$\alpha=30^\circ$\alpha=30^\circ