$\text{1/ a) A = - (-978 + 137) + (-1978 + 599) - (863 + 1599) }$
$\text{A= 978 - 137 - 1978 + 599 - 863 - 1599}$
$\text{A= (978 - 1978) + (599 - 1599) + (-137 - 863)}$
$\text{A= (-1000) + (-1000) + (-1000)}$
$\text{A= -3000.}$
$\text{b) B = - [ - 1234 + (-975 - 347)] + (-234 - 1975) + |-653|}$
$\text{B= - [ - 1234 - 975 - 347] - 234 - 1975 + 653}$
$\text{B= 1234 + 975 + 347 - 234 - 1975 + 653}$
$\text{B= (1234 - 234) + (975 - 1975) + (347 + 653)}$
$\text{B= 1000 - 1000 + 1000}$
$\text{B= 1000.}$
$\text{c) C = -787 . 465 - 787 . 234 + 787 . 779}$
$\text{C = -787 . 465 - 787 . 234 - 787 . (-779)}$
$\text{C = -787 (465 + 234 - 779)}$
$\text{C = -787 . (- 80)}$
$\text{C = 62960.}$
$\text{2/ Ta có :}$
$\text{ - ( - a - 13 ) + (- a + 47) - (b + 25)}$
$\text{= a + 13 - a + 47 - b - 25}$
$\text{= (a - a) - b + (13 + 47 - 25)}$
$\text{= -b + 35}$
$\text{Vậy - ( - a - 13 ) + (- a + 47) - (b + 25) = -b + 35}$
$\text{3/ M = (x - 27) - ( - y + 17) - (x + y - 29)}$
$\text{M = x - 27 + y - 17 - x - y + 29}$
$\text{M = (x - x + y - y) + (-27 - 17 + 29)}$
$\text{M = 0 - 15}$
$\text{M = -15}$
$\text{Vậy giá trị biểu thức không phụ thuộc vào x, y.}$
