Question 948934
Find the angle each line makes with the x-axis.
{{{2x+y=0}}}
{{{y=-2x}}}
{{{m[1]=-2}}}
Slope is change in y over change in x. 
So then the angle is,
{{{tan(alpha)=m}}}
{{{tan(alpha)=-2}}}
{{{alpha=-63.4}}}
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{{{x+3y+4=0}}}
{{{3y=-x-4}}}
{{{y=-x/3-4/3}}}
{{{m[2]=-1/3}}}
{{{tan(beta)=-1/3}}}
{{{beta=-18.4}}}
Now find the difference between the two angles, that's the angle between them,
{{{theta=beta-alpha}}}
{{{theta=-18.4-(-63.4)=highlight(45)}}}