Đáp án:
Bài 5: Tìm x
a) 3 . (x - 12) = 48
x - 12 = 48 : 3
x - 12 = 16
x = 12 + 16
Vậy x = 28
b) 100 - 7 . (x - 5) = 58
7 . (x - 5) = 100 - 58
7 . (x - 5) = 42
x - 5 = 42 : 7
x - 5 = 6
x = 6 + 5
Vậy x = 11
c) $24 + 5x = 7^{5} : 7^{3}$
$24 + 5x = 7^{2}$
$24 + 5x = 49$
$5x = 49 - 24$
$5x = 25$
$x = 25 : 5$
$\text{Vậy x = 5}$
d) $5x - 206 = 2^{4} . 4$
$5x - 206 = 2^{4} . 2^{2}$
$5x - 206 = 2^{6}$
$5x - 206 = 64$
$5x = 64 + 206$
$5x = 270$
$x = 270 : 5$
$\text{Vậy x = 54}$
e) 70 - 5 . (x - 3) = 45
5 . (x - 3) = 70 - 45
5 . (x - 3) = 25
x - 3 = 25 : 5
x - 3 = 5
x = 5 + 3
Vậy x = 8
f) 2x - 138 = 2³ . 3²
2x - 138 = 8 . 9
2x - 138 = 72
2x = 72 + 138
2x = 210
x = 210 : 2
Vậy x = 105
Bài 6: Tìm x:
a) (x - 1)² = 9
(x - 1)² = 3²
⇒ x - 1 = 3
x = 3 + 1
Vậy x = 4
b) (2x - 1)² = 49
(2x - 1)² = 7²
⇒ 2x - 1 = 7
2x = 7 + 1
2x = 8
x = 8 : 2
Vậy x = 4
c) (12 - 2x)² = 16
(12 - 2x)² = 4²
⇒ 12 - 2x = 4
2x = 12 - 4
2x = 8
x = 8 : 4
Vậy x = 2
d) $3^{x-1} = 9$
$3^{x-1} = 3²$
⇒ x - 1 = 2
x = 2 + 1
Vậy x = 3
e) $2 . 5^{x-2} = 250$
$5^{x-2} = 250 : 2$
$5^{x-2} = 125$
$5^{x-2} = 5³$
⇒ x - 2 = 3
x = 3 + 2
Vậy x = 5
f) $3 . 2^{x} + 4 . 2^{x} = 28$
$2^{x} . (3 + 4) = 28$
$2^{x} . 7 = 28$
$2^{x} = 28 : 7$
$2^{x} = 4$
$2^{x} = 2²$
$\text{Vậy x = 2}$
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