Proving |xy-ab| is Less Than Epsilon: Absolute Value Question | Homework Help"

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SUMMARY

The discussion focuses on proving the inequality |xy - ab| < ε(|a| + |b| + ε) given the conditions |x - a| < ε and |y - b| < ε. Participants suggest using the triangle inequality and expanding |xy - ab| into terms like a(y - b) to facilitate the proof. The challenge lies in correctly applying multiplication of inequalities while managing sign considerations. Ultimately, the proof requires careful manipulation of these inequalities to establish the desired result.

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mercuryman
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Homework Statement



Given: |x-a|<ε |y-b|<ε. proove: |xy-ab|<ε(|a|+|b|+ε)


Homework Equations


I need a direction for this proof.


The Attempt at a Solution


I tried by the info: -ε+a<x<ε+a and -ε+b<y<ε+b to ,multiply these inequalities, but it's not true. and i tried with the opposite triangle inequality and it didn't worked.
 
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You can expand |xy-ab| to contain terms like a(y-b) and then use the regular triangle inequality.
The direction multiplication of the inequalities could work, too, but you have to be careful with signs there.
 

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