If a/b >1ab>1, and cc is a positive integer, prove that a/b>(a+c)/(b+c)ab>a+cb+c ?

2 Answers
Jul 22, 2017

See below.

Explanation:

Assuming a > 0, b > 0a>0,b>0, if a/b > 1 rArr a > bab>1a>b then

ab + ac > ab + bcab+ac>ab+bc or

a(b + c) > b(a+c) rArr a/b > (a+c)/(b+c)a(b+c)>b(a+c)ab>a+cb+c

Jul 22, 2017

The assertion fails if a, b < 0a,b<0

Explanation:

The assertion fails if a, b < 0a,b<0

Consider a=-3a=3, b=-2b=2 and c=1c=1

Then:

a/b = (-3)/(-2) = 3/2 > 1ab=32=32>1

(a+c)/(b+c) = (-3+1)/(-2+1) = (-2)/(-1) = 2 > 3/2a+cb+c=3+12+1=21=2>32