X/1*2+X/2*3+/3*4.+X/2002*2003
=X*(1/1*2+1/2*3+1/3*4+.+1/2002*2003)
=X*(1/1-1/2+1/2-1/3+1/3-1/4+.
+1/2001-1/2002+1/2002-1/2003)
=X*(1/1-1/2003)=X*2002/2003
X/1*2+X/2*3+/3*4.+X/2002*2003
=X*(1/1*2+1/2*3+1/3*4+.+1/2002*2003)
=X*(1/1-1/2+1/2-1/3+1/3-1/4+.
+1/2001-1/2002+1/2002-1/2003)
=X*(1/1-1/2003)=X*2002/2003