$\text { a }$, $\text { (x - 2017) . 958 = 0 }$
$\text { ⇔ x - 2017 = 0 }$
$\text { ⇔ x = 0 + 2017 }$
$\text { ⇔ x = 2017}$
$\text { Vậy x = 2017 }$
$\text { b }$, $\text { 959 . (x - 7) = 0 }$
$\text { ⇔ x - 7 = 0 }$
$\text { ⇔ x = 0 + 7 }$
$\text { ⇔ x = 7 }$
$\text { Vậy x = 7 }$
$\text { c }$, $\text { (x - 1) . (x - 2020) = 0 }$
$\text { ⇔ \(\left[ \begin{array}{l}x - 1 = 0\\x - 2020 = 0\end{array} \right.\) }$
$\text { ⇔ \(\left[ \begin{array}{l}x = 1\\x = 2020\end{array} \right.\) }$
$\text { Vậy x ∈ {1 ; 2020} }$
$\text { d }$, $\text { 7x + 4x = 9900 }$
$\text { ⇔ (7 + 4) . x = 9900 }$
$\text { ⇔ 11 . x = 9900 }$
$\text { ⇔ x = 9900 : 11 }$
$\text { ⇔ x = 900 }$
$\text { Vậy x = 900 }$
$\text { e }$, $\text { 2x + x = 6969 }$
$\text { ⇔ (2 + 1) . x = 6969 }$
$\text { ⇔ 3 . x = 6969 }$
$\text { ⇔ x = 6969 : 3 }$
$\text { ⇔ x = 2323 }$
$\text { Vậy x = 2323 }$
