Question

find x,y,z know : 

3x -2y/4 = 2z -4x/3 = 4y - 3z/2   

and x+y+z = 45

Answer 1

Lời giải:

\(\frac{3x-2y}{4}=\frac{2z-4x}{3}=\frac{4y-3z}{2}\)

\(\frac{4(3x-2y)}{16}=\frac{3(2z-4x)}{9}=\frac{2(4y-3z)}{4}\)

\(\frac{12x-8y}{16}=\frac{6z-12x}{9}=\frac{8y-6z}{4}=\frac{12x-8y+6z-12x+8y-6z}{16+9+4}=0\) (tính chất dãy tỉ số bằng nhau)

\(\Rightarrow 12x-8y=6z-12x=8y-6z=0\)

\(\Leftrightarrow 12x=8y=6z\Leftrightarrow \frac{x}{\frac{1}{12}}=\frac{y}{\frac{1}{8}}=\frac{z}{\frac{1}{6}}=\frac{x+y+z}{\frac{1}{12}+\frac{1}{8}+\frac{1}{6}}=\frac{45}{\frac{3}{8}}=120\)

\(\Rightarrow x=120.\frac{1}{12}=10; y=120.\frac{1}{8}=15; z=120.\frac{1}{6}=20\)