(-5,-2,) end point (-7,-5) mid point, how do I find another end point?

Answer 1

Mid-point = (end-point2 - end-point1)/2

So end-point 2 = mid-point + (mid-point - end-point1)
Example, for the x-coordinate,
Xend-point 2 = -7 + (-7-(-5))= -9
Check (-9+-5)/2=-7 OK.

I'll leave the calculation of the y-coordinate to you as an exercise.