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

Find the angle between the lines joining the points $(0, 0), (2, 3)$ and $(2, -2), (3, 5)$.

Two straight lines $3x + 4y = 5$ and $4x - 3y = 15$ intersect at the point $A$. The equations of the lines passing through $(1, 2)$ and intersecting the given lines at $B$ and $C$ such that $AB = AC$ are

Show that two lines $a_{1}x + b_{1}y + c_{1} = 0$ and $a_{2}x + b_{2}y + c_{2} = 0$,where $b_{1}, b_{2} \neq 0$,are perpendicular if $a_{1}a_{2} + b_{1}b_{2} = 0$.

If $S_1$ and $S_2$ are two straight lines such that the reflection of $S_1$ in $S_2$ and the reflection of $S_2$ in $S_1$ coincide,the angle between $S_1$ and $S_2$ is equal to?

The acute angle between the line $4x - 2y + 13 = 0$ and the line which makes equal intercepts with the coordinate axes is