(2)∫a:b = c:d = 2 ∴a=2b,c=2d？ ∴(a+b):b=3b:b=3,(c+d):d=3d:d=3

(3) established. ①∫a:b = c:d？ ∴a=bc/d？ ∴(a-b):b=(bc/d-b):b=c/d？ - 1=(c-d):d

②∫a:b = c:d？ ∴a/b- 1=c/d- 1？ ∴a/b-b/b=c/d-d/d？ ∴(a-b):b=(c-d):d

(4) From the meaning of the question: ①x+y=zm? ②y+z=xm？ ③z+x=ym

By who? ①+②+③de:2(x+y+z)=(x+y+z)m∴(2-m)(x+y+z)= 0？ ∴m=2 or x+y+z=0.

If x+y+z=0, then x+y=-z? ∴m=(x+y)/z=(-z)/z=- 1

To sum up: m=- 1 or 2.

Second, (1)

(2)>

? (1) For any true fraction, the numerator and denominator are greater than the original number plus a positive number.

? ② As shown in the figure.

? ∫a:b is a true fraction, and M is a positive number ∴ A < b? ∴am<； bm？ That's s (b)

? ∴s(a)+s(b)<； S(A)+S(C)

That's ab+am

a(b+m)& lt； b(a+m)？

(a+m):(b+m) > A: B?

Personal opinion, for reference only.