The obtuse angle between the lines $y = -2$ and $y = x + 2$ is .....$^o$

If the angle between two lines is $\frac{\pi}{4}$ and the slope of one of the lines is $\frac{1}{2},$ find the slope of the other line.

The slope of a line is double the slope of another line. If the tangent of the angle between them is $\frac{1}{3},$ find the slopes of the lines.

If the lines $y = 3x + 1$ and $2y = x + 3$ make equal angles with the line $y = mx + 4$,then $m = $ . . .

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 $ac =$

The acute angle between the lines given by $y - \sqrt{3}x + 1 = 0$ and $\sqrt{3}y - x + 7 = 0$ is (in $^{\circ}$)