Find the equation of the line which passes through (-4,1) and is at an angle of 135° with the positive direction of the x axis.

The angle essentially gives the slope.  If you consider, slope is a measure of the steepness of a line, a lot like a hill, which will go up at a certain angle.  To use it for the slope, we need to take tangent function (from trigonometry) of the angle:tan135 = -1
So, in the equation for the line, slope = m = -1
So, we have m = -1 with a point on the line (-4,1).
Various ways to get the equation from there.  We could put this information into the equationy=mx+b:1 = -1*-4 + bSo, we can solve that for b:
1 = 4 + b
b = -3
So, then, we have m and b.  So, we can write the equation for the line:y = -x - 3