Question 937614
{{{1-2+3-4+"..."+49-50+49-48+47-46+"..."+1=highlight(0)}}}
There is more than one way to get to that answer.
 
If you are studying arithmetic sequences, you may be expected to split that sum into three sums of arithmetic sequences,
{{{sum( 2i-1, i=1, i=25 )=1+3+5+"..."+45+47+49=25*(1+49)/2=625}}} , and
{{{sum( 2i, i=1, i=25 )=2+4+6+"..."+46+48+50=25*(2+50)/2=650}}} , or
{{{sum( 2i, i=1, i=24)=2+4+6+"..."+46+48=24*(2+48)/2=600}}} ,
and calculate it as
{{{1-2+3-4+"..."+49-50+49-48+47-46+"..."+1=(1+3+5+"..."+45+47+49)-(2+4+6+"..."+46+48+50)+(49+47+45+"..."5+3+1)-(48+46+"..."+6+4+2)=625-650+625-600=0}}}  , or
{{{1-2+3-4+"..."+49-50+49-48+47-46+"..."+1=(1+3+5+"..."+45+47+49)-(2+4+6+"..."+46+48)+50+(49+47+45+"..."5+3+1)-(48+46+"..."+6+4+2)=625-50-600+625-600=0}}} .
If you are not studying arithmetic sequences, it is easier to calculate it as
{{{1-2+3-4+"..."+49-50+49-48+47-46+"..."+1=((1-2)+(3-4)+"..."+(47-48)+(49-50))+((49-48)+(47-46)+"..."+(5-4)+(3-2))+1=25(-1)+24(1)+1=-25+24+1=0}}} ,
or something like that.
You can see that the first bracket is a sum of {{{25}}} terms of the form {{{2i-1-2i=-1}}} for {{{i=1}}} to {{{i=25}}} ,
and that the second bracket is a sum of {{{24}}} terms of the form {{{2i-(2i-1)=1}}} for {{{i=1}}} to {{{i=24}}} .