Đáp án:
$\text{ a) 25 +(-2+x) = 5 }$
$\text{⇔ -2+x = 5 -25 }$
$\text{⇔ -2 + x = -20 }$
$\text{⇔ x = -20 +2 }$
$\text{⇔ x = -18 }$
$\text{Vậy x = -18 }$
$\text{b) l x+3 l = 4 }$
$\text{Th1 : x+3 ≥ 0 ⇔ x ≥ -3 }$
$\text{x+3 = 4 }$
$\text{⇔ x = 4 -3 }$
$\text{ ⇔ x = 1 (thỏa mãn) }$
$\text{Th2 x+3 < 0 ⇔ x < -3 }$
$\text{⇔ -(x+3) =4 }$
$\text{⇔ -x-3 = 4 }$
$\text{⇔ -x = 4+3 }$
$\text{⇔ -x = 7 }$
$\text{⇔ x = -7 (thỏa mãn) }$
$\text{Vậy x ∈ { 1 ; -7}}$
