The acute angle between the lines $x \cos 30^{\circ} + y \sin 30^{\circ} = 3$ and $x \cos 60^{\circ} + y \sin 60^{\circ} = 5$ is (in $^{\circ}$)

The angle between the straight lines $3x + 4y + 9 = 0$ and $x - 7y - 22 = 0$ is

What is the angle in degrees between the lines $x = 9$ and $x - \sqrt{3}y + 7 = 0$?

Show that the equation of the line passing through the origin and making an angle $\theta$ with the line $y=mx+c$ is $\frac{y}{x}=\frac{m \pm \tan \theta}{1 \mp m \tan \theta}$.

The angle between the lines $x \cos \alpha_1 + y \sin \alpha_1 = p_1$ and $x \cos \alpha_2 + y \sin \alpha_2 = p_2$ is

The angle between the lines $x \cos 30^\circ + y \sin 30^\circ = 3$ and $x \cos 60^\circ + y \sin 60^\circ = 5$ is .....$^\circ$