Bài 8:
a, `x^2` - 5x = 0
x ( x - 5 ) = 0
`=>` \(\left[ \begin{array}{l}x=0\\x-5=0\end{array} \right.\)
`=>` \(\left[ \begin{array}{l}x=0\\x=5\end{array} \right.\)
Vậy x ∈ { 0 ; 5 }
b, 5 ( x - 2 ) = 0
x - 2 = 0
x = 0 + 2
x = 2
Vậy x = 2
c, x ( 2 - x ) = 0
`=>` \(\left[ \begin{array}{l}x=0\\2-x=0\end{array} \right.\)
`=>` \(\left[ \begin{array}{l}x=0\\x=2\end{array} \right.\)
Vậy x ∈ { 0 ; 2 }
d, 5 ( 3x - 21 ) = 0
3x - 21 = 0
3x = 21
x = 7
Vậy x = 7
