Question 879963
A(2,7) and Midpoint of AB is M(4,2),  Find point B
Midpoint Pt(x,y):  ( {{{(x[1] + x[2])/2}}}, {{{(y[1] + y[2])/2  )}}})
(2+x)/2 = 4, x = 6
(7+y)/2 = 2, y = -3
B(6,-3)