Answer by Daichik7
Bài 1 :
$a,2/9 .4/15 + 1/9 . 22/15$
`= 1/9 . 8/15 + 1/9 . 22/15`
`=1/9 . (8/15 + 22/15)`
`= 1/9 . 2`
`=2/9`
`b, 9/11 : 2/5 - 2/11 . 5/2`
`=9/11 .5/2 - 2/11 .5/2`
`=5/2 . (9/11 - 2/11)`
`=5/2 . 7/11`
`=35/22`
Bài 2
`(x-7).(x+1/4)=0`
`⇔ x - 7 = 0`
`x + 1/4 = 0`
`⇔ x = 7`
`x = -1/4`
Vậy `x ∈ {7 ; -1/4}`
`#study well`