\[
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\color{#FFFFFF}{\textbf{N}}  
\color{#F5F5F5}{\textbf{O}}  
\color{#EBEBEB}{\textbf{S}}  
\color{#E0E0E0}{\textbf{T}}  
\color{#D6D6D6}{\textbf{A}}  
\color{#CCCCCC}{\textbf{L}}  
\color{#C2C2C2}{\textbf{G}}  
\color{#B8B8B8}{\textbf{I}}  
\color{#AEAEAE}{\textbf{A}}  
\end{array}
\]

`3^2+5x-7=0`

Ta có `:` `a*c=3*(-7)=-21<0`

`=>` Phương trình có 2 nghiệm phân biệt 

Áp dụng Viete `:` 

`{(x_1+x_2=-5/3),(x_1x_2=-7/3):}`

`A=x_1/x_2+x_2/x_1`

`=((x_1+x_2)^2-2x_1x_2)/x_1x_2`

`=((-5/3)^2-2*(-7/3))/(-7/3)`

`=-67/21`

Vậy `A=-67/21`