Tĩm,y,z biết:
a)\(\dfrac{12x-15y}{7}\)=\(\dfrac{20z-12x}{9}\)=\(\dfrac{15y-20z}{11}\)và x+y+z=48
b)\(\dfrac{x+16}{9}\)=\(\dfrac{y-25}{16}\)=\(\dfrac{z+9}{25}\) và \(^{2x^3}\)-1=15
c)\(\dfrac{x}{y+2+1}\)=\(\dfrac{y}{z+x+1}\)=\(\dfrac{z}{x+y-2}\)=x+y+z
d)\(\dfrac{3}{5}\)x=\(\dfrac{2}{3}\)y và \(^{x^2}\)-\(^{y^2}\)= 38
e)\(\dfrac{y+2+1}{x}\)=\(\dfrac{z+x+2}{y}\)=\(\dfrac{x+y+3}{z}\)=\(\dfrac{1}{x+y+z}\)
f)\(\dfrac{1+2y}{18}\)=\(\dfrac{1+4y}{24}\)=\(\dfrac{1+6y}{6x}\)
b: 2x^3-1=15
=>2x^3=16
=>x=2
\(\dfrac{x+16}{9}=\dfrac{y-25}{16}=\dfrac{z+9}{25}\)
=>\(\dfrac{y-25}{16}=\dfrac{z+9}{25}=\dfrac{18}{9}=2\)
=>y-25=32; z+9=50
=>y=57; z=41
d: 3/5x=2/3y
=>9x=10y
=>x/10=y/9=k
=>x=10k; y=9k
x^2-y^2=38
=>100k^2-81k^2=38
=>19k^2=38
=>k^2=2
TH1: k=căn 2
=>\(x=10\sqrt{2};y=9\sqrt{2}\)
TH2: k=-căn 2
=>\(x=-10\sqrt{2};y=-9\sqrt{2}\)
