(a2-49).(a2-81)=0
=>(a2-49)=0 hoặc(a2-81)=0
TH1:(a2-49)=0
=>a2=49
=>a=7
TH2:(a2-81)=0
=>a2=81
=>a=9
Vậy a={7;9}
nhớ k mk nha
\(\left(a^2-49\right)\left(a^2-81\right)=0\)
\(\Leftrightarrow\orbr{\begin{cases}a^2-49=0\\a^2-81=0\end{cases}\Leftrightarrow\orbr{\begin{cases}a^2=49\\a^2=81\end{cases}\Leftrightarrow}\orbr{\begin{cases}a=\pm7\\a=\pm9\end{cases}}}\)
Vậy a={-9;-7;7;9}
có: \(\left(a^2-49\right).\left(a^2-81\right)=0\)
\(\Leftrightarrow\)\(\orbr{\begin{cases}a^2-49=0\\a^2-81=0\end{cases}}\)\(\Leftrightarrow\orbr{\begin{cases}a^2=49\\a^2=81\end{cases}}\)\(\Leftrightarrow\orbr{\begin{cases}a=7\\a=9\end{cases}}\)
vậy....
(a2-49).(a2-81)=0
Goi (a2-49)va (a2-81)la hai thua so muon h cua chung bang 0,
khi va chi khi mot trong hai thua so bang 0.
(a2-49)=0 hoac (a2-81)=0
a2-49=0 a2-81=0
a2=0+49 a2=0+81
a2=49 a2=81
a2=72 a2=92
vay a=7 hay a=9
Ta có : ( a2 -49 ) . ( a2 -81 ) = 0
<=> \(\orbr{\begin{cases}a^2-49=0\\a^2-81=0\end{cases}\Leftrightarrow\orbr{\begin{cases}a^2=49\\a^2=81\end{cases}\Leftrightarrow}\orbr{\begin{cases}a^2=7^2\\a^2=9^2\end{cases}}\Leftrightarrow\orbr{\begin{cases}a=7\\a=9\end{cases}}}\)
Vậy a = { 7 ; 9 }