Proving e^x ≥ 1 + x for All x ∈ [0,∞)

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In summary, the conversation discusses how to prove that the inequality e^x >= 1 + x is true for all values of x in the interval [0,inf). The suggested approach is to define f(x) = e^x - x - 1 and find its derivative, f'(x). By using the first derivative test and analyzing the intervals where f'(x) is greater than or equal to zero, it can be concluded that the inequality holds for any x greater than zero. The exception is when x = 0, where the inequality is already valid.
  • #1
nuuc
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how would i prove that e^x >= 1 + x for all x in [0,inf)?
 
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  • #2
where are your thoughts?
hint: expand out to see.
 
  • #3
Define f(x) = e^x - x - 1. What can f'(x) tell us?
 
  • #4
morphism said:
Define f(x) = e^x - x - 1. What can f'(x) tell us?
like morphism stated, now what u have to do is just find f'(x)= (e^x-x-1)', what is f'(x) now?,
After that look at what interval the function f(x) is always greater or equal to zero, using the first derivative test,can you do it? and the result surely should be for any x greater than zero. It is obvious that for x=0 the >= sing is valid.
 

1. What is e^x and how is it related to the proof?

e^x is a mathematical constant, also known as Euler's number, which is approximately equal to 2.71828. It is used in the proof as it is the base of the natural logarithm, ln, which is a fundamental function in calculus.

2. Why is it important to prove e^x ≥ 1 + x?

Proving e^x ≥ 1 + x for all x ∈ [0,∞) is important because it is a fundamental inequality in mathematics and has many applications in fields such as calculus, physics, and economics. It also helps to understand the behavior of exponential functions.

3. How does the proof for e^x ≥ 1 + x work?

The proof uses mathematical induction, which is a technique for proving a statement for all natural numbers. It starts by showing that the statement is true for the first natural number, and then assuming it is true for n, it is proved for n+1. This process is repeated until the statement is proved for all natural numbers.

4. Can the proof be extended to other intervals or values of x?

Yes, the proof can be extended to other intervals or values of x. However, it may require additional steps or adjustments to the initial proof. For example, if we want to prove e^x ≥ 1 + x for all x ∈ [-1, ∞), we would need to consider a different base case and adjust the inductive step accordingly.

5. Are there any real-life applications of this proof?

Yes, there are many real-life applications of this proof. For example, in economics, the proof can be used to show that the continuous compounding of interest will always result in a higher return compared to simple interest. In physics, it is used to model exponential growth and decay in natural phenomena. It is also used in computer science and engineering to analyze algorithms and the complexity of problems.

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