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 two lines $y - 2x = 9$ and $x + 2y = -7$ is .....$^o$.

If the equation of a line having a slope $m$ $(m \in \mathbb{Z})$,passing through $(1, 1)$ and making an angle of $\tan^{-1}\left(\frac{5}{7}\right)$ with the line $x + y - 3 = 0$ is $ax + y + c = 0$,then $ac =$

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

If the lines $mx + 2y + 1 = 0$ and $2x + 3y + 5 = 0$ are perpendicular to each other,then what is the value of $m$?

Let the angle between the lines $x-2y+3=0$ and $kx-y+2=0$ be $45^{\circ}$. If $k_1, k_2$ $(k_1 > k_2)$ are two distinct real values of $k$,then $k_1-2=$