-1 + 2 - 3 + 4 - 5 + 6 - … - 999 + 1000
= -(1 + 3 + 5 + … + 999) + (2 + 4 + 6 + … + 1000)
= -((2 - 1) + (4 - 1) + (6 - 1) + … + (1000 - 1)) + 2 (1 + 2 + 3 + … + 500)
= -((2 + 4 + 6 + … + 1000) - 500) + 2 (1 + 2 + 3 + … + 500)
= -(2 (1 + 2 + 3 + … + 500) - 500) + 2 (1 + 2 + 3 + … + 500)
Let S = 1 + 2 + 3 + … + 500. Then this sum is equal to
= -(2S - 500) + 2S
= -2S + 500 + 2S
= 500
and multiplying by 4 gives 2000.
Answer:
[tex]4\times \left(\left(-1+2-3+4-5+6-7+1000\right)\right)[/tex]
[tex]calculate\: within \: the \:parentheses[/tex]
[tex]-1+2=1[/tex]
[tex]=1-3+4-5+6-7+1000[/tex]
[tex]1-3=-2[/tex]
[tex]=-2+4-5+6-7+1000[/tex]
[tex]-2+4=2[/tex]
[tex]=-3+6-7+1000[/tex]
[tex]3-7+1000[/tex]
[tex]=-4+1000[/tex]
[tex]=996[/tex]
[tex]Multiply:-[/tex]
[tex]4\times996[/tex]
[tex]=3984[/tex]
--------------------------
Hope it helps..
Have a great day!!
