Bài 1 :
a) 37 . 52 + 37 . 48 = 37 . (52+48) = 37 . 100 = 3700
b) 20 + 5x = $5^{7}$ : $5^{6}$
20 + 5x = $(5)^{7-6}$
20 + 5x = $5^{1}$
20 + 5x = 5
5x = 5 - 20
5x = -15
x = -15 : 5
x = -3
c) $5^{2x-3}$ - 2 .$5^{2}$ = $5^{2}$ . 3
$5^{2x-3}$ = 2 .$5^{2}$ + $5^{2}$ . 3
$5^{2x-3}$ = $5^{2}$ . (3 + 2) = $5^{2}$ . 5 = $5^{3}$
2x - 3 = 3
2x = 3 + 3
2x = 6
x = 6 : 2
x = 3
⇒ x = 3
Bài 2 :
a) 3 . |x + 7| = 21
⇒ x + 7 = 21 : 3
⇒ x + 7 = 7
⇒ $\left \{ {{x - 7 = 27} \atop {x - 7 = -27}} \right.$
⇒ $\left \{ {{x = 27 + 7} \atop {x = -27 + 7}} \right.$
⇒ $\left \{ {{x = 34} \atop {x = -20}} \right.$
Vậy x ∈ {34; -20}
b) 20 + 5x = $5^{7}$ : $5^{5}$
20 + 5x = $5^{7-5}$
20 + 5x = $5^{2}$
20 + 5x = 25
5x = 25 - 20
5x = 5
x = 5 : 5
x = 1
c) $5^{2x-3}$ - 2 .$5^{2}$ = $5^{2}$ . 3
$5^{2x-3}$ = 2 .$5^{2}$ + $5^{2}$ . 3
$5^{2x-3}$ = $5^{2}$ . (3 + 2) = $5^{2}$ . 5 = $5^{3}$
2x - 3 = 3
2x = 3 + 3
2x = 6
x = 6 : 2
x = 3
⇒ x = 3
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