Tim x,y,z
a/ \(\frac{x}{y}\)=\(\frac{7}{3}\)va 5x-2y=87
b/\(\frac{x}{19}\)=\(\frac{y}{21}\)và 2x-y=34
c/\(\frac{x^3}{8}\)=\(\frac{y^3}{64}\)=\(\frac{z^3}{216}\)va \(x^2\)+\(y^2\)+\(z^2\)=14
đ/\(\frac{2x+1}{5}\)=\(\frac{3y-2}{7}\)=\(\frac{2x+3y-1}{6x}\)
dễ vãi