Question

\(\dfrac{x}{3}=\dfrac{y}{4},\dfrac{y}{5}=\dfrac{z}{7}\) và 2x+3y-z=124

 

Answer 1

\(\dfrac{x}{3}=\dfrac{y}{4}=>\dfrac{1}{5}.\dfrac{x}{3}=\dfrac{1}{5}.\dfrac{y}{4}=>\dfrac{x}{15}=\dfrac{y}{20}\left(1\right)\\ \dfrac{y}{5}=\dfrac{z}{7}=>\dfrac{1}{4}.\dfrac{y}{5}=\dfrac{1}{4}.\dfrac{z}{7}=>\dfrac{y}{20}=\dfrac{z}{28}\left(2\right)\\ \left(1\right);\left(2\right)=>\dfrac{x}{15}=\dfrac{y}{20}=\dfrac{z}{28}=\dfrac{2x+3y-z}{2.15+3.20-28}=\dfrac{124}{62}=2\\ =>x=2.15=30;y=2.20=40;z=2.28=56\)