a, 5 . ( -8 ) . ( -2 ) . ( -3 )
= 5 . 8 . 2 . ( -3 )
= ( 5 . 8 ) . ( -3 . 2 )
= 40 . ( -6 )
= -240
b, 53 - ( -51 ) + ( -53 ) + 49
= 53 + 51 - 53 + 49
= ( 53 - 53 ) + ( 51 + 49 )
= 0 + 100
= 100
c, 100 + ( +430 ) + 2145 + ( -530 )
= 100 + 430 + 2145 - 530
= ( 2145 + 100 ) - ( 540 - 430 )
= 2245 - 100
= 2145
d, - 75 . ( 18 - 65 ) - 65 . ( 75 - 18 )
= ( -75 ) . 18 + 75 . 65 - 65 . 75 + 65 . 18
= 65 . 18 - 75 . 18
= 18 . ( -10 )
= -180
e, A = 2 + ( -3 ) + 4 + ( -5 ) + ... + 2008 + ( -2009 ) + 2010 + ( -2011 ) + 2012
A = 2 - 3 + 4 - 5 + ... + 2008 - 2009 + 2010 - 2011 + 2012
A = ( 2 - 3 ) + ( 4 - 5 ) + ... + ( 2010 - 2011 ) + 2012 ( có 1005 cặp số )
A = ( -1 ) + ( -1 ) + ... + ( -1 ) + 2012 ( có 1005 số hạng -1 )
A = 1005 . ( -1 ) + 2012
A = 2012 - 1005
A = 1007
Vậy A = 1007