Real analysis Help - Intermediate Value Thrm

In summary: The sum of two continuous functions is continuous and same for a multiple, but I don't see how this applies to me using the IVT. The problems requires I use that theorem.
  • #1
CrazyCalcGirl
15
0

Homework Statement



Use the Intermediate Value Theorem to show that the equation 2^x=3x has a solution c element of (0,1)

Homework Equations





The Attempt at a Solution

Ok I know this theorem is usually very easy, but I've never done one where I couldn't easily solve for x and plug in the end points to look for a sign change. I already graphed 2^x and 3x on my calculator and found that there is a solution in (0,1) now I just need to prove it.

My only thoughts were this

let f(x)= 2^x
Let g(x) = 3x

f(0)=2^0=1 and f(1)=2^1=2
g(0)=3x0=0 and G(1)= 3x1=3

f(0)>g(0) and f(1)<g(1) so this means at some point they must cross each other and there must exist c element of (0,1) such that 2^x=3x.

Is this even right at all or anyone have a better idea?
 
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  • #2
You do this trick a lot in analysis when considering two functions being equal at a point or on an interval:

Define
[tex]f(x):=2^x-3x[/tex]

What do you know about the sum of two continuous functions? Or rather, the sum of a continuous function and a multiple of a continuous function?
 
Last edited:
  • #3
I know the sum of two continuous functions is continuous and same for a multiple, but I don't see how this applies to me using the IVT. The problems requires I use that theorem.

If you think the way I did it is wrong how about this...?

If I use your idea to let f(x)= 2^x-3x now I can just plug in the endpoints of my interval.

f(0)=1
f(1)=-1

Since they have opposite signs the IVT says there must be a real root c in (0,1).

We just got into continuity and we haven't actually learned anything about sums or multiples yet. We are not allowed to use anything on the homework we have not done in class.
 
  • #4
By Plugging in the endpoints, you are correct =]
 
  • #5
hmm both ways I did it I plugged in the endpoints.. so if the first way correct that I originally posted or is the second way correct where you set f(x)= 2^x-3x?

Thanks : )
 
  • #6
CrazyCalcGirl said:
If I use your idea to let f(x)= 2^x-3x now I can just plug in the endpoints of my interval.

f(0)=1
f(1)=-1

Since they have opposite signs the IVT says there must be a real root c in (0,1).

That is the correct part.
 

FAQ: Real analysis Help - Intermediate Value Thrm

What is the Intermediate Value Theorem?

The Intermediate Value Theorem is a fundamental theorem in real analysis that states that if a continuous function f(x) is defined on a closed interval [a,b] and takes on values f(a) and f(b) at the endpoints, then for any value C between f(a) and f(b), there exists at least one point c in the interval (a,b) where f(c) equals C. In other words, the function takes on every value between f(a) and f(b) at some point within the interval.

How is the Intermediate Value Theorem used in real analysis?

The Intermediate Value Theorem is used to prove the existence of roots of equations, such as finding the solution to f(x) = 0. It is also used to prove the existence of maximum and minimum values of a function on a closed interval, which is important in optimization problems. Additionally, it is used to show that a function is continuous on a given interval.

What are the necessary conditions for the Intermediate Value Theorem to hold?

In order for the Intermediate Value Theorem to hold, the function must be continuous on the closed interval [a,b]. This means that the function has no breaks or jumps in its graph and can be drawn without lifting the pencil. The endpoints f(a) and f(b) must also be defined on the interval.

Can the Intermediate Value Theorem be applied to all functions?

No, the Intermediate Value Theorem only applies to continuous functions. If a function is not continuous, it may have "holes" or "jumps" in its graph, making it impossible to find a point where the function takes on a specific value between two endpoints.

Are there any variations of the Intermediate Value Theorem?

Yes, there are generalizations and variations of the Intermediate Value Theorem. For example, the Bolzano-Weierstrass Theorem states that a bounded, real-valued function must have at least one real root. The Intermediate Value Theorem for derivatives states that if a function is continuous on a closed interval and its derivative is positive at one endpoint and negative at the other, then the derivative must equal 0 at some point in between.

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