2. Tính.
1) A = 2 – 4 + 6 – 8 + … + 1998 – 2000
2) B = 2 – 4 – 6 + 8 + 10 – 12 – 14 + 16 + … + 1994 – 1996 – 1998 + 2000
2. Tính. 1) A = 2 – 4 + 6 – 8 + … + 1998 – 2000 2) B = 2 – 4 – 6 + 8 + 10 – 12 – 14 + 16 + … + 1994 – 1996 – 1998 + 2000
By Hailey
`1)A=2−4+6−8+….+1998−2000`
`A=(2−4)+(6−8)+….+(1998−2000) (500 )`
`A=(−2)+(−2)+….+(−2)`
`A=(−2).500`
`A=−1000`
`2)B=2−4−6+8+10−12−14+16+….+1994−1996−1998+2000`
`B=(2−4−6+8)+(10−12−14+16)+….+(1994−1996−1998+2000)`
`B=0+0+….+0`
`B=0`
$#JAW#$
`1 ) A = 2 – 4 + 6 – 8 + …. + 1998 – 2000`
`A = ( 2 – 4 ) + ( 6 – 8 ) + …. + ( 1998 – 2000 )` `( 500` nhóm `)`
`A = ( – 2 ) + ( – 2 ) + …. + ( – 2 )`
`A = ( – 2 ) . 500`
`A = – 1000`
Vậy , `A = – 1000 .`
`2 ) B = 2 – 4 – 6 + 8 + 10 – 12 – 14 + 16 + …. + 1994 – 1996 – 1998 + 2000`
`B = ( 2 – 4 – 6 + 8 ) + ( 10 – 12 – 14 + 16 ) + …. + ( 1994 – 1996 – 1998 + 2000 )`
`B = 0 + 0 + …. + 0`
`B = 0`
Vậy , `B = 0 .`