Question

Tính tổng :

B=1 -5 +9 -13 +.....................+ 2009 -2013+2017 -2021

Answer 1

B = 1 -5 +9 -13 +.....................+ 2009 -2013+2017 -2021

=(1 -5) +(9 -13) +.....................+ (2009 -2013)+(2017 -2021)

( 253 cặp )

= -4 + ( - 4 ) +... + ( -4 )

( 253 số -4 )

= -4 . 253

=-1012

Answer 2

1-5+9-13 +...+ 2009-2013+2017-2021

=(1-5) + (9-13) + ... + (2009-2013) + (2017-2021)

=-4 x 253

=-1012

Answer 3

B= 1-5+9-13 +......+ 2009-2013+2017-2021

=  (1-5) + (9-13) + ....... + (2009-2013) + (2017-2021)

=  -4 x 253

=  -1012