text: help with geometry/algebra(midpoint and slope stuff)? m is the midpoint of the coordinate of the midpoint of ab. find the missing endpoint m(10,12) a(4,-4) find the coordinates of b .. i have a test on this tomorrow and i so dont get it.. help please :) i think you set it up like   4+y/2  ,  -4-y/2  but i dunno what to do after that.. i ont even know if that part is right ... please help ,e if you can .. and show the work so i can see how you got the answer pleaseeeeee you find midpoint by adding the 2 x-coordinates of the endpoints and dividing by 2, and doing the same for the y-coordinates.  so if you know the midpoint and one end, it looks like this (assume the other endpoint is (x,y):  (4+x)/2 = 10; (-4+y)/2 = 12  multiply by 2: 4+x=20; -4+y=24  so x=16 and y=28