Áp dụng tính chất dãy tỉ số bằng nhau ta có:

x/3 = y/5 = x+y/3+5 = 16/8 = 2

=> x = 6 ; y = 10

x² + y² = 36 + 100 = 136        

suy ra x-1/2+1=y-2/3+1=z-3/4+1 suy ra x+1/2=y+1/3=z+1/4 = K Ta có x=2K-1;y=3K-1;z=4k-1 mà x-2y+3z =-10

x/2=2y/3=3z/4=k,x=2k,y=3k:2,z=4k:3 ta có 2k-3k:2=15=1k:2=15;k=15.2=30;x=2.30=60;y=3.30:2=45,z=4.30:=40_x-y-z=-25

\(2^{x+1}.3^y=12^x=>2^{x+1}.3^y=2^{2x}.3^x=>\frac{2^{2x}}{2^{x+1}}=\frac{3^y}{3^x}=>2^{x-1}=3^{y-x}=>x-1=y-x=0\)

=>x=y=1

vậy x+y=2

\(\frac{x}{12}=\frac{y}{9}=\frac{z}{8}\) => \(\frac{x-y}{12-9}=\frac{15}{3}=5\)=> x = 60 ; y= 45 ; z=40 => x-y-z = 60-45-40 =-25

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

Áp dụng t/c dãy tỉ số=nhau:

\(\frac{x}{2}=\frac{y}{\frac{3}{2}}=\frac{z}{\frac{4}{3}}=\frac{x-y}{2-\frac{3}{2}}=\frac{15}{\frac{1}{2}}=30\)

=>x/2=30=>x=60

y/3/2=30=>y=30.3/2=45

z/4/3=30=>z=30.4/3=40

Vậy x-y-z=60-45-40=-25