数学高手进啊～

1).
(a+b)/b = a/b + 1 = 2/3 + 1 = 5/3

2).
设 x/3 = y/4 = z/5 = k
x = 3k
y = 4k
z = 5k
(x + y + z)/(x + y - z) = (3k + 4k + 5k)/(3k + 4k - 5k) =
12k / 2k =
6

a/b=2/3，a+b是五份，b是三份，所以(a+b)/b=5/3
第二问跟楼上的一样

a=2 b=3 a+b/b=5

1.设a=2t,b=3t
则(a+b)/b=(2t+3t)/3t=5t/3t=5/3.
2.设x/3=y/4=z/5=t
则x=3t,y=4t,z=5t
故(x+y+z)/(x+y-z)=(3t+4t+5t)/(3t+4t-5t)=12t/2t=6.

利用和比 等比性质直接出来了
a/b=2/3 就有 (a+b)/b=(2+3)/3=5/3

x/3=y/4=z/5
则
x/3=y/4=z/5=（x+y+z)/(3+4+5)=(x+y-z)/(3+4-5)

（x+y+z)/12=(x+y-z)/2

（x+y+z)/(x+y-z)=12/2=6

1)a=2/3b a+b/b=(2/3b+b)/b=5/3
2)x=3/5z y=4/5z
(x+y+z)/(x+y-z)=(3/5z+4/5z+z)/(3/5z+4/5z-z)
=6