Question

Tìm hai số xy âm biết rằng \(\frac{x}{2}=\frac{y}{5}\)  và x.y = 40

Answer 1

x/2=y/5=k suy ra x=2k; y=5k

5kx2k=40

10k^2=40

k^2=40:10=4

k=-2(x;y<0)

ta có; x=-2x2=-4

y=-2x5=-10

Answer 2

\(\frac{x}{2}=\frac{y}{5}\Leftrightarrow\frac{x.y}{2.5}=\frac{40}{10}=4\)

\(\Rightarrow\frac{x}{2}=4\Rightarrow x=8\)

\(\Rightarrow\frac{y}{5}=4\Rightarrow y=20\)

Answer 3

\(\frac{x}{2}=\frac{y}{5}=>=\frac{x}{2.k}=\frac{y.}{5.k}\left(k\right)khác0\)

mà x.y=40

=>2k.5k=40

=>(2.5)k=40

10k=40

k=40:10

k=4

=>\(\frac{x}{2k}=\frac{x}{5k}=\frac{x}{2.4}=\frac{y}{5.4}=\frac{x}{8}=\frac{y}{20}\)

=>x.k=x.4=8

x=2

y.k=y.4=20

y=5