a) -(-1998)-(-721 + 2998)
= 1998 + 721 - 2998
= (1998 - 2998) + 721
= -1000 + 721
= -279
b) -5².13.(-2)³.(-1)^2n-1
= -25.13.(-8).(-1) (vì: 2n-1 lẻ)
= 25.13.(-8)
= -200.13
= -2600
c) (-31).25 + 31.119 - 31.(-6)
= 31.(-25) + 31.119 - 31.(-6)
= 31.[(-25) + 119 - (-6)]
= 31.100
= 3100
d) -79.(73 - 27) - 73.(-79 + 27)
= -79.73 + (-79).(-27) - 73.(-79) - 73.27
= [-79.73 - 73.(-79)] + 79.27 - 73.27
= 0 + 27.(79 - 73)
= 27.6
= 162