bài 2)
16) `( 7-x) . ( x+19) = 0`
⇒ `7 - x = 0` `hoặc` `x` + `19` = `0`
`x = 7 - 0` `hoặc` `x = 0 - 19`
`x = 7` `hoặc` `x = -19`
`Vậy` `x` ∈ { `7` ; `-19`}
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15) `(x-2).(x+4)=0`
⇒`x - 2 = 0` `hoặc` `x+4=0`
`x = 0+2` `hoặc` `x = 0-4`
`x = 2` `hoặc` `x = -4`
`Vậy` `x∈{2;-4}`
-------------------------------------------------------------
13) `-12(x-5)+7(3-x)=5`
`-12x - (-12).5 + 7.3 - 7x = 5`
`-12x+ 60 + 21 - 7x = 5`
`x ( -12 -7) + (60+21)=5`
`x .-19+ 81 = 5`
`x . -19 = 5 - 81`
`x . -19 =-76`
`x =-76:(-19)`
`x = 4`
------------------------------------------------------------
8) `| x - 2 | = 3`
⇒ `x - 2 = 3` `hoặc` `x-2=-3`
`x = 3+2` `hoặc` `x = -3+2`
`x =5` `hoặc` `x=-1`
Vậy `x∈{5;-1}`
--------------------------------------------------------------
9) `| x -3|-7=13`
`| x -3| = 13+7`
`| x -3| = 20`
⇒ `x-3 =20` `hoặc` `x-3=-20`
`x =20+3` `hoặc` `x = -20+3`
`x = 23` `hoặc` `x=-17`
`Vậy` `x∈{23;-17}`
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10) `72-3. |x+1| =9`
`3.|x+1|=72-9`
`3.|x+1|=63`
`|x+1|=63:3`
`|x+1|= 21`
⇒`x+1=31` `hoặc` `x+1=-21`
`x =21-1` `hoặc` `x =-21-1`
`x =20` `hoặc` `x =-22`
`Vậy` `x∈{30;-32}`
