Proving the Inequality: logx < x^1/2 for x>1

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In summary, to prove the inequality logx < x^1/2, we can use the properties of logarithms and exponents. This inequality can also be represented visually by plotting the graphs of y = logx and y = x^1/2 on the same coordinate plane. Its significance lies in its demonstration of the relationship between logarithmic and exponential functions and its applications in various fields. This inequality can be generalized to other logarithmic and exponential functions, with exceptions at x = 1 and x = e.
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ha11
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How can prove logx< x^1/2 for x>1
 
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  • #2
What have you tried so far? Perhaps induction will work
 
  • #3
Here's one approach:

Define [tex]f(x) = \sqrt{x} - \ln(x)[/tex].

See if you can show that [tex]f(1) > 0[/tex] and [tex]f'(x) \geq 0[/tex] for [tex]x \geq 1[/tex].

That would do it. Do you see why?

[Edit] Oops, that won't work, because it isn't true that [tex]f'(x) \geq 0[/tex] for [tex]x \geq 1[/tex]!

So try this instead-- find the minimum value of f by solving [tex]f'(x) = 0[/tex]. If the minimum is positive (and it is), then you are done.
 
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  • #4
thanks
 

FAQ: Proving the Inequality: logx < x^1/2 for x>1

1) How do you prove the inequality logx < x^1/2?

To prove this inequality, we can use the properties of logarithms and exponents. First, we can rewrite the inequality as logx < √x. Then, we can raise both sides to the power of e, since the exponential function is always increasing. This gives us x < e^√x. Finally, we can use the fact that e^√x is always greater than √x to conclude that x < e^√x < e^x. Therefore, we have proved the inequality logx < x^1/2.

2) Can you provide a visual representation of this inequality?

Yes, we can represent this inequality graphically by plotting the graphs of y = logx and y = x^1/2 on the same coordinate plane. We can see that the graph of y = logx is always below the graph of y = x^1/2, which visually shows that logx < x^1/2 for all x > 0.

3) What is the significance of this inequality in mathematics?

This inequality is significant because it demonstrates the relationship between logarithmic and exponential functions. It also has applications in various fields such as calculus, number theory, and statistics.

4) Can this inequality be generalized to other logarithmic and exponential functions?

Yes, this inequality can be generalized to other logarithmic and exponential functions. For example, we can prove that logx < x^a for any real number a > 0. The proof follows a similar approach as the one shown above.

5) Are there any exceptions to this inequality?

Yes, there are exceptions to this inequality. For example, when x = 1, logx = 0 and x^1/2 = 1, so the inequality does not hold. Additionally, when x = e (the base of the natural logarithm), logx = 1 and x^1/2 = √e, so the inequality is also not true. However, the inequality holds for all other positive values of x.

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