Question

(1) 5+6=11 6^2-5^2=11

Answer 1

(2n-1)+2n=4n-1,(2n)^2-(2n-1)^2=4n-1=(2n-1)+(2n)

1^2-2^2+3^2-4^2+5^2 .-98^2+99^2-100^2+101^2

=-(2^2-1^2)-(4^2-3^2)-...-(100^2-99^2)+101^2

=-(1+2)-(3+4)-...-(99+100)+101^2

=-(1+2+3...+100)+101^2

=-100*(100+1)/2+101^2

=5100