geometry
posted by Beatrice .
If a line segment has endpoints A(3x+5, 3y) and B(x1, y) what are the coordinates of the midpoint AB?

the midpoint is just the average of the endpoints:
M = ( ((3x+5)+(x1))/2 , (3y+(y))/2 )
= ((4x+4)/2 , 2y/2)
= (2x+2,y)