find the lengths of the medians of the triangle with vertices A( 1,2,3) B(-2,0,5) C(4,1,5) Solution Mid-point formula [ (x1+x2)/2, (y2+y1)/2 ] AC (0,1) (5,4) = E(5/2, 3) AB (0,1) (8,1) =D( 4, 1) BC( (8,1) ,(5,4)= F(13/2, 5/2) distance d² = ( x2- x1)² + ( y2-y1)² AF²= (13/2- 8)²+(5/2-1)²=(-3./2)²+(3/2)²= 9/4 + 9/4=18/4 =9/2 AF= 3v2/2.