To find the equation of a line using two coordinate points, use the slope intercept formula, (y2-y1)/(x2-x1). Using this formula, plug in your values from the two coordinates (-5, -5) and (1, -3). This would look like this: (-3-(-5))/(1-(-5)) When simplified, you should get 2/6 or 1/3 as your slope or m value. Now that you have your slope, now use your slope intercept equation y=mx+b and plug in your known values. Since you know the m value is 1/3 and you can use one of your set of points to plug into the x and y values, you can plug in these values and solve for b (the coordinate you use doesn't matter but I'm just using the (1,-3)). This would look like this: -3=1/3(1)+b
When you simplify, you should get -3=1/3+b and when you subtract both sides by 1/3, you should get b=-10/3.
Now that you have your m and b values, you can conclude that your equation for the line would be y=1/3x-10/3
Cos(x) = 1 at 0 and 2pi 360 and -360 is the same angle as 2pi so all of the above if you start at 0 and make a complete circle (360) you will be back at point 0.
