原式=(1-2)(1+2)+(3-4)(3+4)+.+(99-100)(99+100)+101^2
=-(1+2)-(3+4).-(99+100)+101^2
=-(1+2+3+4+...+99+100)+101^2
=-(1+100)*100/2+(100+1)^2
=-5050+100^2+200+1
=5151