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.

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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 equation`y=mx+b`:

`1 = -1*-4 + b`

So, 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`

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