\(-3x=7y=21z\Rightarrow\frac{x}{-\frac{1}{3}}=\frac{y}{\frac{1}{7}}=\frac{z}{\frac{1}{21}}\)
\(\Rightarrow\frac{5x}{-\frac{5}{3}}=\frac{10y}{\frac{10}{7}}=\frac{6z}{\frac{2}{7}}\)
Theo t/c dãy tỉ số = nhau ta có:
\(\frac{5x}{-\frac{5}{3}}=\frac{10y}{\frac{10}{7}}=\frac{6z}{\frac{2}{7}}=\frac{5x+10y+6z}{-\frac{5}{3}+\frac{10}{7}+\frac{2}{7}}=\frac{4}{\frac{1}{21}}=4.21=84\)
\(\Rightarrow\frac{x}{-\frac{1}{3}}=84\Rightarrow x=-\frac{1}{3}.84=-28\)
\(\Rightarrow\frac{y}{\frac{1}{7}}=84\Rightarrow y=\frac{1}{7}.84=12\)
\(\Rightarrow\frac{z}{\frac{1}{21}}=84\Rightarrow z=\frac{1}{21}.84=4\)
Vậy x=-28; y=12; z=4.
Ta co : -3x=7x=21x=>x/-1/3=x/1/7=x/1/21=>5x/-5/3=10y/10/7=6z/2/7 va 5x+1oy+6z=4
Ap dung tinh chat day ti so bang nhau :
5x/-5/3=10y/10/7=6z/2/7=5x+10y+6z/-5/3+10/7+2/7=4/1/21=84
Suy ra :x/-1/3=8x=>x=-28
y/1/7=84=>y=12
z/1/21=84=>z=4
**** nhe