Prove 0<a<1, 0<b<1, then ab<a

  • #1
knowLittle
312
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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1. How can we prove the inequality ab < a when 0 < a < 1 and 0 < b < 1?

To prove this inequality, we can start by noting that since 0 < a < 1, we know that a is a positive number less than 1. Similarly, since 0 < b < 1, we know that b is also a positive number less than 1. Multiplying two numbers less than 1 together will always result in a number smaller than either of the original numbers, hence ab < a.

2. Why is it important to consider the range of values for a and b in this inequality?

Considering the range of values for a and b is important in this inequality because it helps us understand the behavior of the variables within a specific range. In this case, when a and b are both between 0 and 1, their product will always be smaller than a. This understanding is crucial in various mathematical and scientific applications.

3. Can you provide a concrete example to illustrate this inequality?

Sure! Let's take a = 0.5 and b = 0.3 as an example. When we multiply these values together, we get ab = 0.5 * 0.3 = 0.15. Since 0.15 is smaller than 0.5 (a), the inequality ab < a holds true.

4. How does the concept of fractions play a role in proving this inequality?

The concept of fractions is fundamental in proving this inequality because when a and b are both fractions between 0 and 1, their product will always be a smaller fraction. This is due to the fact that multiplying two fractions results in a smaller fraction, making the inequality ab < a valid.

5. Are there any exceptions to this inequality when 0 < a < 1 and 0 < b < 1?

No, there are no exceptions to this inequality when a and b are both between 0 and 1. The inequality ab < a holds true for all values of a and b within this range, as multiplying two numbers less than 1 will always result in a smaller number than either of the original numbers.

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