+885 A line segment has one endpoint at (3,9) and midpoint at (1,2) . What is the sum of the coordinates of the other endpoint?
+129850 We have
( 3 + x) / 2 = 1 and (9 + y ) / 2 = 2
Multiply both side by 2
3 + x = 2 and 9 + y = 4
subtract 3 from both sides subtract 9 from both sides
x = -1 y = -5
This is the other endpoint
And the sum of its coordinates = -6
