Question

Tìm a,b \(\in N\) biết

c) \(2^a+342=7^b\)

d) \(2^a+80=3^b\)

Answer 1

\(a,\) Vì \(7^b\) lẻ, 342 chẵn nên \(2^a\) lẻ 

\(\Rightarrow a=0\\ \Rightarrow7^b=343=7^3\\ \Rightarrow b=3\)

Vậy \(\left(a;b\right)=\left(0;3\right)\)

\(b,\) Vì \(3^b\) lẻ, 80 chẵn nên \(2^a\) lẻ

\(\Rightarrow a=0\\ \Rightarrow3^b=81=3^4\\ \Rightarrow b=4\)

Vậy \(\left(a;b\right)=\left(0;4\right)\)