Toán Lớp 7: a) 9,27 ≤ 3^x ≤ 243
b) 3 × 8^x – 2 × 2^3x – 64 = 0
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Toán Lớp 7: a) 9,27 ≤ 3^x ≤ 243
b) 3 × 8^x – 2 × 2^3x – 64 = 0
Comments ( 2 )
a)9.27le3^xle243
=>3^2. 3^3le3^xle3^5
=>3^5le3^xle3^5
=>5lexle5
=>x=5
Vậy x=5
b)3.8^x-2.2^(3x)-64=0
3.2^(3x)-2.2^(3x)=0+64
2^(3x).(3-2)=64
2^(3x).1=64
2^(3x)=64:1
2^(3x)=64
2^(3x)=2^6
=>3x=6
=>x=6:3
=>x=2
Vậy x=2
@Ki ng
Giải đáp và lời giải
a) 9.27\le3^x\le243
=>3^(2).3^3\le3^x\le3^5
=>3^5\le3^x\le3^5
=>x=5
Vậy x=5
b) 3.8^x-2.2^(3x)-64=0
=>3.8^x-2.(2^3)^x=0+64
=>3.8^x-2.8^x=64
=>8^x.(3-2)=64
=>8^x=8^2
=>x=2
Vậy x=2