7:8:9
內項積=外項積,
24y=18x, x:y=24:18=4:3
6z=10y, y: z= 6: 10= 3:5
x: y: z= 4: 3: 5=4r:3r:5r
(x+y):(y+z):(z+x)=7r: 8r: 9r = 7: 8: 9