a) $3^{x}$ . 3 = 81
⇔ $3^{x}$ = 81 : 3
⇔ $3^{x}$ = 27
⇔ $3^{x}$ = $3^{3}$
⇒ x = 3
Vậy x = 3
b) $4^{x}$ : 4 = 16
⇔ $4^{x - 1}$ = $4^{2}$
⇒ x - 1 = 2
⇔ x = 2 + 1
⇔ x = 3
Vậy x = 3
c) 3 . $2^{x}$ = 48
⇔ $2^{x}$ = 48 : 3
⇔ $2^{x}$ = 16
⇔ $2^{x}$ = $2^{4}$
⇒ x = 4
Vậy x = 4
d) $2^{x+3}$ + $2^{x}$ = 144
⇔ $2^{x}$ . $2^{3}$ + $2^{x}$ = 144
⇔ $2^{x}$ . 8 + $2^{x}$ = 144
⇔ $2^{x}$ . (8 + 1) = 144
⇔ $2^{x}$ . 9 = 144
⇔ $2^{x}$ = 144 : 9
⇔ $2^{x}$ = 16
⇔ $2^{x}$ = $2^{4}$
⇒ x = 4
Vậy x =4
e) $3^{x}$ + $3^{x + 2}$ = 2430
⇔ $3^{x}$ + $3^{x}$ . $3^{2}$ = 2430
⇔ $3^{x}$ + $3^{x}$ . 9 = 2430
⇔ $3^{x}$ . (1 + 9) = 2430
⇔ $3^{x}$ . 10 = 2430
⇔ $3^{x}$ = 2430 : 10
⇔ $3^{x}$ = 243
⇔ $3^{x}$ = $3^{5}$
⇒ x = 5
Vậy x = 5
f) $2^{x+3}$ - $2^{x}$ = 224
⇔ $2^{x}$ . $2^{3}$ - $2^{x}$ = 224
⇔ $2^{x}$ . 8 - $2^{x}$ = 224
⇔ $2^{x}$ . (8 - 1) = 224
⇔ $2^{x}$ . 7 = 224
⇔ $2^{x}$ = 224 : 7
⇔ $2^{x}$ = 32
⇔ $2^{x}$ = $2^{5}$
⇒ x = 5
Vậy x = 5
g) $2^{x}$ + $2^{x + 1}$ = 96
⇔ $2^{x}$ + $2^{x}$ . 2 = 96
⇔ $2^{x}$ . (1 + 2) = 96
⇔ $2^{x}$ . 3 = 96
⇔ $2^{x}$ = 96 : 3
⇔ $2^{x}$ = 32
⇔ $2^{x}$ = $2^{5}$
⇒ x = 5
Vậy x = 5
h) sai đề
i) $3^{x+2}$ - $3^{x+1}$ + $3^{x}$ = 189
⇔ $3^{x}$ . (9 - 3 + 1) = 189
⇔ $3^{x}$ . 7 = 189
⇔ $3^{x}$ = 189 : 7
⇔ $3^{x}$ = 27
⇔ $3^{x}$ = $3^{3}$
⇒ x = 3
Vậy x = 3
