finding endpoints don't quite understand it. M-LN if L coordinates are -3,-1 and M coordinates are 0,1
If I understand you correctly,
L(-3,-1) is one end point, and M(0,1) is the midpoint
let N(a,b) be the other endpoint
then (a-3)/2 = 0 and (b-1)/2 = 1
a-3 = 0 and b-1 = 2 , (I multiplied both sides by 2 in each equation)
a = 3 and b = 3
the other endpoint is N(3,3)
check:
is (-3+3)/2 = 0 ? yes
is (-1+3)/2 = 1 ? yes