The vector [tex]v_1=(4,1)[/tex] is parallel to the line [tex]y=4x+2[/tex]
and the vector [tex]v_2(-1,1)[/tex] is parallel to the line [tex]y=-x+3[/tex].
On one hand [tex]v_1v_2=(-1)4+1^2=-3[/tex].
On the other hand
[tex]v_1v_2=\vert v_1\vert\vert v_2\vert cos\theta\\=\sqrt{17}\sqrt{2}\cos\theta[/tex]
Equating we get [tex]\sqrt{34}\cos\theta=-3[/tex].
so [tex]\theta=\cos^{-1}\dfrac{-3}{\sqrt{34}}=120\text{ degrees}[/tex]
