Is My Proof That ab<a Correct Given 0<a<1 and 0<b<1?

In summary, the proof that \( ab < a \) is correct for the conditions \( 0 < a < 1 \) and \( 0 < b < 1 \) relies on the properties of multiplication involving positive numbers less than one. Since both \( a \) and \( b \) are fractions, their product \( ab \) will always be less than either \( a \) or \( b \), confirming that \( ab < a \) holds true under the given constraints.
  • #1
knowLittle
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3
I would like some feedback on my proof.

Can I just say that :
0< a<1 ... [1]
0<b<1 ... [2]

multiplying [2] by 'a' everywhere, then I get
0<ab<a

And, we prove that ab<a?
 
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  • #2
Yes. But you need to note that the multiply does not reverse the inequality signs because "a" is always positive.
(and don't you want a final QED?)
 
  • #3
knowLittle said:
I would like some feedback on my proof.

Can I just say that :
0< a<1 ... [1]
0<b<1 ... [2]

multiplying [2] by 'a' everywhere, then I get
0<ab<a

And, we prove that ab<a?
Actually, if 0 < a and 0 < b < 1, then ab < a. a does not have to be less than 1.

-Dan
 
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  • #4
I don't want to be overkill on this, but the proof will depend on the axioms and rules you're going by.
You may, though, move the a to the other side and factor.
 
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  • #5
Thank you all!
 
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FAQ: Is My Proof That ab<a Correct Given 0<a<1 and 0<b<1?

Is my proof that ab < a correct given 0 < a < 1 and 0 < b < 1?

Yes, your proof is correct. Since both a and b are positive numbers less than 1, their product ab will also be less than a. This is because multiplying by a fraction (a number between 0 and 1) reduces the value of a.

Why does ab < a hold true when 0 < a < 1 and 0 < b < 1?

The inequality ab < a holds true because multiplying a number a (where 0 < a < 1) by another number b (where 0 < b < 1) results in a product that is smaller than a. This is due to the properties of fractions: multiplying by a fraction reduces the value.

Can you provide an example to illustrate why ab < a?

Sure, consider a = 0.5 and b = 0.6. Both numbers are between 0 and 1. The product ab = 0.5 * 0.6 = 0.3, which is indeed less than 0.5 (the value of a). This demonstrates that ab < a.

Is the inequality ab < a always true for any values of a and b between 0 and 1?

Yes, the inequality ab < a is always true for any values of a and b between 0 and 1. This is because both a and b are positive fractions, and their product will always be a smaller fraction, thus less than a.

How can I formally prove that ab < a given 0 < a < 1 and 0 < b < 1?

To formally prove that ab < a given 0 < a < 1 and 0 < b < 1, consider that since b is between 0 and 1, we can write b as b = 1 - c where 0 < c < 1. Then ab = a(1 - c) = a - ac. Since ac is positive (because both a and c are positive and less than 1), it follows that a - ac < a, hence ab < a.

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