=(2-1)(2+1)+(3-1)(3+1)+.+(100-1)(100+1)
=2^2-1+3^2-1+...+100^2-1
=(1+2^2+3^2+...+100^2)-100
=[100*(100+1)(200+1)]/6-100
=338350-100
=338250
=(2-1)(2+1)+(3-1)(3+1)+.+(100-1)(100+1)
=2^2-1+3^2-1+...+100^2-1
=(1+2^2+3^2+...+100^2)-100
=[100*(100+1)(200+1)]/6-100
=338350-100
=338250