Proving ab - a - b + 2 > 1 in Simple Algebra: Tips and Hints

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The discussion centers on proving the inequality ab - a - b + 2 > 1 for all values of a > 1 and b > 1. The transformation of the inequality into the equivalent form (b - 1)(1 - a) < 0 is crucial for understanding the conditions under which the original statement holds true. Participants confirm that recognizing the relationship between a and b is key to solving the problem effectively. The insights shared provide a clear path to proving the inequality through algebraic manipulation.

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Chen
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Hi,

I need to prove that for every a > 1 and b > 1 the following holds:

ab - a - b + 2 > 1

Can someone please throw me some hints? :)

Thanks,
Chen
 
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It's equivalent to proving

ab - a - b + 1 > 0
<=>
a(b - 1) - b + 1 > 0
<=>
-a(b - 1) + b - 1 < 0
<=>
(b - 1)(1 - a) < 0.
 
Argh, I was close but didn't see that! Thanks. :-)
 

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