a) \(\dfrac{-9}{x}=\dfrac{-x}{\dfrac{4}{49}}\)
\(\Rightarrow-x^2=-\dfrac{36}{49}\)
\(\Rightarrow-x=-\dfrac{6}{7}\) , vậy \(x=\dfrac{6}{7}\)
b) \(\dfrac{x}{3}=\dfrac{y}{5}=\dfrac{y-x}{5-3}=\dfrac{9}{2}=4,5\)
\(\Rightarrow\left\{{}\begin{matrix}x=13,5\\y=22,5\end{matrix}\right.\)
c) \(2x=3y\Leftrightarrow\dfrac{x}{3}=\dfrac{y}{2}=\dfrac{x+y}{3+2}=\dfrac{20}{5}=4\)
\(\Rightarrow\left\{{}\begin{matrix}x=4\cdot3=12\\y=4\cdot2=8\end{matrix}\right.\)
a, \(\dfrac{-9}{x}=\dfrac{-x}{\dfrac{4}{49}}\Rightarrow-x^2=-\dfrac{36}{49}\)
\(\Rightarrow x^2=\dfrac{36}{49}\Rightarrow x=\pm\dfrac{6}{7}\)
b, Áp dụng tính chất của dãy tỉ số bằng nhau ta có:
\(\dfrac{x}{3}=\dfrac{y}{5}=\dfrac{y-x}{5-3}=\dfrac{9}{2}=4,5\)
\(\Rightarrow\left\{{}\begin{matrix}x=4,5.3=13,5\\y=4,5.5=22,5\end{matrix}\right.\)
c,Ta có: \(2x=3y\Rightarrow\dfrac{x}{3}=\dfrac{y}{2}\)
Áp dụng tính chất của dãy tỉ số bằng nhau ta có:
\(\dfrac{x}{3}=\dfrac{y}{2}=\dfrac{x+y}{3+2}=\dfrac{20}{5}=4\)
\(\Rightarrow\left\{{}\begin{matrix}x=4.3=12\\y=4.2=8\end{matrix}\right.\)
Chúc bạn học tốt!!!