https://i.imgur.com/fbhAwaV.jpg
Ta có: a, b, c tỉ lệ với 2, 3, 5
\(\Rightarrow\frac{a}{2}=\frac{b}{3}=\frac{c}{5}.\)
Đặt \(\frac{a}{2}=\frac{b}{3}=\frac{c}{5}=k\Rightarrow\left\{{}\begin{matrix}a=2k\\b=3k\\c=5k\end{matrix}\right.\)
Có: \(A=\frac{a+2b-c}{a-2b+3c}.\)
\(\Rightarrow A=\frac{2k+2.3k-5k}{2k-2.3k+3.5k}\)
\(\Rightarrow A=\frac{2k+6k-5k}{2k-6k+15k}\)
\(\Rightarrow A=\frac{\left(2+6-5\right).k}{\left(2-6+15\right).k}\)
\(\Rightarrow A=\frac{3k}{11k}\)
\(\Rightarrow A=\frac{3}{11}.\)
Vậy \(A=\frac{3}{11}.\)
Chúc bạn học tốt!