Giải thích các bước giải:
Bài `3.`
`a)`
`3/7-1/21x=1/3`
`=>1/21x=3/7-1/3`
`=>1/21x=9/21-7/21`
`=>1/21x=2/21`
`=>x=2/21:1/21`
`=>x=2/21 . 21/1`
`=>x=2`
Vậy `x=2`
`b)`
`7/6-x:3/4=1/12`
`=>x:3/4=7/6-1/12`
`=>x:3/4=14/12-1/12`
`=>x:3/4=13/12`
`=>x=13/12 . 3/4`
`=>x=13/16`
Vậy `x=13/16`
`c)`
`(x-2/7)(x+3/4)=0`
`=>[(x-2/7=0),(x+3/4=0):}`
`=>[(x=0+2/7),(x=0-3/4):}`
`=>[(x=2/7),(x=-3/4):}`
Vậy `x\in{2/7;-3/4}`
`d)`
`(-5/4x+3,25)[3/5-(-5/2x)]=0`
`=>(-5/4x+325/100)(3/5+5/2x)=0`
`=>(-5/4x+13/4),(3/5+5/2x)=0`
`=>[(-5/4x+13/4=0),(3/5+5/2x=0):}`
`=>[(-5/4x=0-13/4),(5/2x=0-3/5):}`
`=>[(-5/4x=-13/4),(5/2x=-3/5):}`
`=>[(x=-13/4 : (-5)/4),(x=-3/5:5/2):}`
`=>[(=-13 / 4 . (-4)/5),(x=-3/5 . 2/5):}`
`=>[(x=13/5),(x=-6/25):}`
Vậy `x\in{13/5;-6/25}`
