∴a+b≥0

∵|a|=8，|b|=4

∴ 1*a=8 b=4

2*a=8 b=-4

∴ To sum up, a+b= 12or4.

2.∵|x+y| and |2y-3| are antonyms.

∴x+y=2y-3=0 (both absolute values are non-negative, and if two non-negative numbers are opposite, they are both 0).

∴2y=3 y=3/2

x = -3/2

∴ 2x+y=- 1.5

3. A and B are antonyms, B and C are reciprocal, and the absolute value of the sum of D and E is equal to 2.

∴b=-a c = 1/b =-a/ 1 | d+e | = 2

Original formula =-2bc+(a+b) ÷ bc+d+e.

=-2(-a) (- 1/a) +0 2

=-2+0 2

1* Original formula =-2+2=0

2* Original formula =-2-2=-4

To sum up, the original formula is equal to 0 or -4.