Question

Tìm các số a,b,c biết: a/3 = b/4 = c/5 và a.c=60

Answer 1

Đặt \(\dfrac{a}{3}=\dfrac{b}{4}=\dfrac{c}{5}=k\Rightarrow a=3k,b=4k,c=5k\)

Có: \(3k.5k=60\)

\(\Rightarrow15k^2=60\Rightarrow k^2=4\Rightarrow k=\pm2\)

TH1: \(k=2\)

\(\Rightarrow\left\{{}\begin{matrix}a=3k=6\\b=4k=8\\c=5k=10\end{matrix}\right.\)

TH2: \(k=-2\)

\(\Rightarrow\left\{{}\begin{matrix}a=3k=-6\\b=4k=-8\\c=5k=-10\end{matrix}\right.\)

Answer 2

Đặt a/3=b/4=c/5=k

=>a=3k; b=4k; c=5k

Ta có: ac=60

\(\Leftrightarrow15k^2=60\)

\(\Leftrightarrow k^2=4\)

TH1: k=2

=>a=6; b=8; c=10

TH2: k=-2

=>a=-6; b=-8; c=-10