Question

Tìm x, biết:
a) \(3^{x+1}=81\) b) \(3^x+3^{x+1}=324\)

Answer 1

a) \(3^{x+1}=81\)

\(\Rightarrow3^{x+1}=3^4\)

\(\Rightarrow x+1=4\)

\(\Rightarrow x=3\)

Vậy \(x=3\)

b) \(3^x+2^{x+1}=324\)

\(\Rightarrow3^x+3^x.3=324\)

\(\Rightarrow3^x.\left(1+3\right)=324\)

\(\Rightarrow3^x.4=324\)

\(\Rightarrow3^x=81\)

\(\Rightarrow3^x=3^4\)

\(\Rightarrow x=4\)

Vậy \(x=4\)

Answer 2

a, Ta có \(3^{x+1}=81\Rightarrow3^{x+1}=3^4\)

\(\Rightarrow x+1=4\Rightarrow x=3\)

Vậy x= 3

b, Ta có \(3^x+3^{x+1}=324\Rightarrow3^x+3^x.3=324\)

\(\Rightarrow3^x.\left(1+3\right)=324\Rightarrow3^x.4=324\)

\(\Rightarrow3^x=81\Rightarrow3^x=3^4\Rightarrow x=4\)

Vậy x=4

 

Answer 3

3\(^{x+1}\)=81

\(\Rightarrow\)3\(^{x+1}\)=3\(^4\)

\(\Rightarrow\) x+1=4

\(\Rightarrow\) x=4-1

\(\Rightarrow\)x=3