a) 2^n=128/4=32=2^5\(\Rightarrow\)n=5
b)3^n+1 :9=81\(\Rightarrow\)3^n.3 :9=81\(\Rightarrow\)3^n:3=81\(\Rightarrow\)3^n =243=3^5\(\Rightarrow\)n=5
c) 15^n:15=(3^2)^2:3^4=3^4:3^4=1\(\Rightarrow\)15^n=15=15^1\(\Rightarrow\)n=1
a, <=> 2^n = 128/4 = 32
<=> 2^n = 2^5
<=> n =5
b,<=> 3^(n+1) = 81.9= 729
<=> 3^(n+1) = 3^6
<=> n+1 = 6 <=> n =5
c, <=> 15^(n-1) = 1
<=> 15^(n-1) = 15^ 0
<=> n-1 = 0 <=> n =1
2n . 4 =128
2n =128:4
2n = 32
2n = 25
<=> n = 5
a) \(2^n\cdot4=128\Rightarrow2^n\cdot2^2=2^7\Rightarrow2^{n+2}=2^7\Rightarrow n+2=7\Rightarrow n=7-2\Rightarrow n=5\)
b) \(3^{n+1}:9=81\Rightarrow3^{n+1}:3^2=3^4\Rightarrow3^{n+1-2}=3^4\Rightarrow n+1-2=4\Rightarrow n-1=4\Rightarrow n=5\)
c) \(15^{n-4}=9^2:3^4\Rightarrow15^{n-4}=9^2:9^2\Rightarrow15^{n-4}=15^0\Rightarrow n-4=0\Rightarrow n=4\)
Bạn của mình lại làm thế này nè:
a) 2n. 4=128
2n=128:4
2n=32
2n=25
=>n=5
b) 3n+1:9=81
3n+1=81.9
3n+1=34.32
3n+1=36
=>n+1=6
n=6-1
n=5
c) 15n-2=92:34
15n-2=34.34
15n-2=1
=>n-2=0
n=2