Tính: a, (–90 + 150) – (10 – 50). b, 1 – 2 – 3 + 4 + 5 – 6 – 7 + 8 + …+ 997 – 998 – 999 + 1000.
Giải thích
a, (–90 + 150) – (10 – 50)
= –90 + 150 – 10 + 50
= (–90 – 10) +(150 + 50)
= –100 + 200 = 100.
b, 1 – 2 – 3 + 4 + 5 – 6 – 7 + 8 + …+ 997 – 998 – 999 + 1000.
= (1 – 2 – 3 + 4) + (5 – 6 – 7 + 8) +…+ (997 – 998 – 999 + 1000)
=0 + 0 + …+ 0 = 0.