\(\frac{15}{x-9}=\frac{20}{y-12}\Rightarrow\frac{x-9}{15}=\frac{y-12}{20}\Leftrightarrow\frac{x}{15}-\frac{3}{5}=\frac{y}{20}-\frac{3}{5}\)

\(\Rightarrow\frac{x}{15}=\frac{y}{20}\)

\(\Rightarrow\frac{x^2}{15^2}=\frac{x}{15}.\frac{y}{20}=\frac{1200}{300}=4=2^2\Rightarrow x^2=2^2.15^2=30^2\)

\(\Rightarrow x=30\text{ hoặc }x=-30\)

+TH1: x = 30

\(\frac{y}{20}=\frac{x}{15}\Rightarrow y=\frac{20.x}{15}=\frac{20.30}{15}=40\)

\(\frac{40}{z-24}=\frac{15}{30-9}=\frac{5}{7}\Rightarrow z=\frac{40.7}{5}+24=80\)

+TH2: x = -30

\(\frac{y}{20}=\frac{x}{15}=-\frac{30}{15}=-2\Rightarrow y=-2.20=-40\)

\(\frac{40}{z-24}=\frac{15}{-30-9}=-\frac{15}{3}\Rightarrow z=\frac{-3.40}{15}+24=16\)

\(\dfrac{15}{x-9}=\dfrac{20}{y-12}=\dfrac{40}{z-24}\)

\(\Rightarrow\dfrac{x-9}{15}=\dfrac{y-12}{20}=\dfrac{z-24}{40}=k\)

\(\Rightarrow\left(15k+9\right)\left(20k+12\right)=1200\)

\(\Rightarrow3.4\left(5k+3\right)\left(5k+3\right)=1200\)

\(\Rightarrow\left(5k+3\right)\left(5k+3\right)=1200:3:4\)

\(\Rightarrow\left(5k+3\right)^2=100\)

\(\Rightarrow\left[{}\begin{matrix}5k+3=10\\5k+3=-10\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}k=\dfrac{7}{5}\\k=\dfrac{-13}{5}\end{matrix}\right.\)

+) Với \(k=\dfrac{7}{5}\)

\(\Rightarrow\left\{{}\begin{matrix}x=\dfrac{7}{5}.15+9\\y=\dfrac{7}{5}.20+12\\z=\dfrac{7}{5}.40+24\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}x=30\\y=40\\z=80\end{matrix}\right.\)

+) Với \(k=\dfrac{-13}{5}\)

\(\Rightarrow\left\{{}\begin{matrix}x=\dfrac{-13}{5}.15+9\\y=\dfrac{-13}{5}.20+12\\z=\dfrac{-13}{5}.40+24\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}x=-30\\y=-40\\z=-80\end{matrix}\right.\)

Vậy ................................

Chúc bạn học tốt!

dạng nhân này thì bạn đặt =k sẽ ra cả nha,mk ngại đánh lắm

x=80 (x chớ ko phải y ghi nhầm đề rồi)

y=-40

z=16

mk hoc lop 6 soryy ko giup duoc

ai giúp mk vs

Câu a và câu  b khó quá nên minh chí giúp bn câu b thôi!

c chứ ko phải b nha bn mình viết nhầm