Question

Bài 2: Tìm a,b,c:

a) \(\dfrac{a}{3}\)=\(\dfrac{b}{5}\)=\(\dfrac{c}{6}\); x.y.z=720

b)\(\dfrac{a}{5}\)=\(\dfrac{b}{7}\); a.b=140

Answer 1

ý a) sao đang \(a,b,c\) lại thành \(x,y,z\) ? :DD??

Answer 2

b: Đặt \(\dfrac{a}{5}=\dfrac{b}{7}=k\)

\(\Leftrightarrow\left\{{}\begin{matrix}a=5k\\b=7k\end{matrix}\right.\)

Ta có: ab=140

nên \(35k^2=140\)

\(\Leftrightarrow k^2=4\)

Trường hợp 1: k=2

\(\Leftrightarrow\left\{{}\begin{matrix}a=5k=10\\b=7k=14\end{matrix}\right.\)

Trường hợp 2: k=-2

\(\Leftrightarrow\left\{{}\begin{matrix}a=5k=-10\\b=7k=-14\end{matrix}\right.\)