Đáp án:
Giải thích các bước giải:
`800-(x+20).3=20`
`( x + 20 ) .3 = 800 - 20`
`(x + 20 ) . 3 = 780`
`x + 20 = 780 : 3`
`x +20 = 260`
`x = 260 - 20`
`x = 240`
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
`3(x-15)-45=15`
`3(x-15) = 15 + 45`
`3(x-15)= 60`
`x - 15 = 60 :3`
`x - 15 = 20`
`x = 20 +15`
`x = 35`
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __ _ _ _ _ _ _ _
`(3x-12)+3^2=69`
`(3x-12) + 9 = 69`
`3x -12 = 69 - 9`
`3x - 12 = 60`
`3x = 60 + 12`
`3x = 72`
`x = 72 : 3`
`x = 24`
