a, x² - 7x = 0
=> x . (x-7) = 0
=> \(\left[ \begin{array}{l}x=0\\x-7=0\end{array} \right.\)
=> \(\left[ \begin{array}{l}x=0\\x=7\end{array} \right.\)
Vậy x ∈ {0;7}
b, x + x + x + 81 = -3 - x
=> 3x + 81 = -3 - x
=> 4x = -84
=> x = - 21
Vậy x = -21
c, (-1).(-3).(-6).2.x = 72
=> -36x = 72
=> x = -2
Vậy x = -2
d, x².(x - 7) = 0
=> \(\left[ \begin{array}{l}x²=0\\x-7=0\end{array} \right.\)
=> \(\left[ \begin{array}{l}x=0\\x=7\end{array} \right.\)
Vậy x ∈ {0;7}
e, (x + 3)² . ( -6 - 2x)³ = 0
=> \(\left[ \begin{array}{l}(x + 3)²=0\\( -6 - 2x)³=0\end{array} \right.\)
=> \(\left[ \begin{array}{l}x + 3=0\\-6 - 2x=0\end{array} \right.\)
=> \(\left[ \begin{array}{l}x=-3\\x=-3\end{array} \right.\)
Vậy x ∈ {-3}
