Question

Tìm x , y , z biết : \(\frac{x}{3}=\frac{y}{4}\)

\(\frac{y}{5}=\frac{z}{7}\)

Và \(2x+3y-z=186\)

Answer 1

\(\frac{x}{3}=\frac{y}{4};\frac{y}{5}=\frac{z}{7}\Rightarrow\frac{x}{15}=\frac{y}{20};\frac{y}{20}=\frac{z}{28}\Rightarrow\frac{x}{15}=\frac{y}{20}=\frac{z}{28}\)

áp dung tính chất của dãy tỉ số bằng nhau ta có:

\(\frac{x}{15}=\frac{y}{20}=\frac{z}{28}=\frac{2x+3y-z}{2.15+3.20-28}=\frac{186}{62}=3\)

suy ra: \(\frac{x}{15}=3\Rightarrow x=45\)

\(\frac{y}{20}=3\Rightarrow y=60\)

\(\frac{z}{28}=3\Rightarrow z=84\)

Answer 2

\(\frac{x}{3}=\frac{y}{4};\frac{y}{5}=\frac{z}{7}\Rightarrow\frac{x}{15}=\frac{y}{20};\frac{y}{20}=\frac{z}{28}\)

\(\frac{x}{15}=\frac{y}{20}=\frac{z}{28}=\frac{2x+3y-z}{2.15+3.20-28}=\frac{186}{62}=3\)

=>\(\frac{x}{15}=3\Rightarrow3.15=45\)

    \(\frac{y}{20}=3\Rightarrow3.20=60\)

    \(\frac{z}{28}=3\Rightarrow3.28=84\)

 

Answer 3

x = 45

y = 60

z = 84