Câu `1:B`
Vì `1: (-1 2/3)=1:(-5/3)= -3/5=(-3)/5`
Câu `2:A`
`5cm:20cm=5/20`
Câu `3:B`
`12/x=(-4)/9`
`(-4)x=108`
`x=(-27)`
Câu `4:C`
Ta có : `\hat{xOy}=\hat{xOz}.2=42.2=84^o`
Bài `1:`
Bài `1:`
`a)7/12-8/9+5/12`
`=(7/12+5/12)-8/9`
`=1-8/9`
`=1/9`
`b)-3/4.(-55/9).8/11`
`=(-55/12).8/11`
`=(-440)/132`
`c)3 1/5:2,4-35/42 . 20%`
`=16/5:12/5-5/6 . 1/5`
`=4/3-1/6`
`=8/6-1/6`
`=7/6`
`d)(-4)/9 . 5/13+8/13 . (-4)/9-10/18`
`=(-4)/9 . (5/13+8/13)-5/9`
`=(-4)/9 . 1-5/9`
`=(-4)/9-5/9`
`=(-1)`
Bài `2` :
`a)(-7)/8+x=1/12`
`x=1/12-(-7)/8`
`x=8/96-(-84)/96`
`x=92/96=23/24`
`b)7/4-3/4.(x+2/3)=(-1)`
`1.(x+2/3)=(-1)`
`x+2/3=(-1)`
`x=(-1)-2/3`
`x=(-5)/3`
`c)(1/5-x)^2=9/16`