原式等于=12+18-17-15
=12+18+(-17)+(-15)
=8
原式等于=-2/3-1/6+1/4 -1/2
= -8/6 +1/4
= -13/12
简便运算:
(1):=49-(23.75+25.25)+18.7-5.7
= 49-49 +18.7-5.7
=13
(2):解=1 - 5/15+3/15-13/15-1/2-39/20
= 1-(5/12-3/15+13/15)-1/2-39/20
= 1-1 -1/2-39/20
= -49/20
原式等于=12+18-17-15
=12+18+(-17)+(-15)
=8
原式等于=-2/3-1/6+1/4 -1/2
= -8/6 +1/4
= -13/12
简便运算:
(1):=49-(23.75+25.25)+18.7-5.7
= 49-49 +18.7-5.7
=13
(2):解=1 - 5/15+3/15-13/15-1/2-39/20
= 1-(5/12-3/15+13/15)-1/2-39/20
= 1-1 -1/2-39/20
= -49/20