Bài 1:Tính hợp lí nếu có thể:
a,3-7+12-15
b,(-5)+6+9-12
c,-29.(85-47)-85.(47-29)
d,31-[26-(209+35)]
Bài 1:Tính hợp lí nếu có thể: a,3-7+12-15 b,(-5)+6+9-12 c,-29.(85-47)-85.(47-29) d,31-[26-(209+35)]
By Kinsley
By Kinsley
Bài 1:Tính hợp lí nếu có thể:
a,3-7+12-15
b,(-5)+6+9-12
c,-29.(85-47)-85.(47-29)
d,31-[26-(209+35)]
Bài 1:
a, 3-7+12-15
=(3-15)+12-7
=-12+12-7
=0-7
=-7
b, ,(-5)+6+9-12
=1+9-12
=10-12
=-2
c, ,-29.(85-47)-85.(47-29)
=-29.85+29.47-85.47+85.29
=85.(-29+29)+47.(29-85)
=85.0+47.(-56)
=0+(-2632)
=-2632
d,31-[26-(209+35)]
=31-[26-144]
=31+188
=219
a) 3 – 7 + 12 – 15 = (3 + 12) – (7 + 15) = 15 – 22 = -7
b) (-5) + 6 + 9 – 12 = [(-5) + 6] + (9 – 12) = 1 + (-3) = -2
c) -29.(85 – 47) – 85.(47 – 29) = -1102 – 1530 = -2632
d) 31 – [26 – (209 + 35)] = 31 – (26 – 244) = 31 – (-218) = 249