Show that Eqs. (6.6) through (6.11) are not altered by a shift of the origin of x, y, z ...

Show that Eqs. (6.6) through (6.11) are not altered by a shift of the origin of x, y, z from the center of twist to any point within the cross section defined by x=a and y=b, and where a and b are constants. [Hint: The displacements are now expressed as   and w=w(x,y).]