Bài `1:`
`a)`
`2/3 + (-1/3) + 7/15`
`= (2 + (-1))/3 + 7/15`
`= 1/3 + 7/15`
`= 5/15 + 7/15`
`= (5 + 7)/15`
`= 12/15`
`= 4/5`
`b)`
`3/8 xx 23/14 - 3/8 xx 9/14 + (1/8)^0`
`= 3/8 xx (23/14 - 9/14) + 1`
`= 3/8 xx ((23 - 9)/14) + 1`
`= 3/8 xx 1 + 1`
`= 3/8 + 1`
`= 3/8 + 8/8`
`= (3 + 8)/8`
`= 11/8`
Bài `2:`
`a)`
`5/3 - 2/3 x = 1`
`2/3 x = 5/3 - 1`
`2/3 x = 5/3 - 3/3`
`2/3 x = (5 - 3)/3`
`2/3 x = 2/3`
`x = 2/3 : 2/3`
`x = 2/3 xx 3/2`
`x = (2 xx 3)/(3 xx 2)`
`z = 6/6`
`x = 1`
`Vậy: x = 1`
`b)`
`x/5 = 20/x`
`=> x . x = 5 . 20`
`=> x^2 = 100`
`=> x^2 = (+-10)^2`
`=>` \(\left[ \begin{array}{l}x = 10\\x = -10\end{array} \right.\)
`Vậy: x ∈ {10; -10}`
