=1/2x(1/1x2-1/2x3)+1/2x(1/2x3-1/3x4)+……+1/2x(1/48x49-1/49x50)
=1/2x(1/1x2-1/2x3+1/2x3-1/3x4+……+1/48x49-1/49x50)
=1/2x(1/1x2-1/49x50)
=306/1225