1.令x/2=y/4=z/7=t,则x=2t,y=4t,z=7t, 带入2x+y+3z=58,即4t+4t+21t=58,得t=2,从而 x=4,y=8,z=14 , x+y/x+z=12/18=2/3
2.由ab:bc:ac=10:12:15 ,可知ac：bc=15/12,即a：b=5/4 ,ab:ac=10:15,即b:c=2/3,从而a:b:c=5:4:6
3 由1/2*a:1/3*b=1:2,可得a:b=3:1,又b:c=2:3从而a:b：c=6:2:3
4
5 设三边分别为a,b,c 则有a:b:c=3:4:5,从而可设a=3t,b=4t,c=5t,从而3t+4t+5t=84,得t=7,从而三边的长为a=21,b=28,c=35
6 设三个数为a,b,c 从而a:b:c=3:4:5,设a=3t,b=4t,c=5t,再由三个数的平均数为25,即a+b+c=25*3=75, 从而3t+4t+5t=75,得t=25/4 ,从而三个数为a=75/4,b=25, c=125/4