Proving the Limit of f(ax) with Delta Epsilon

In summary, the problem is asking for a proof of the limit of a function f(ax) as x approaches 0 being equal to the limit of f(x) as x approaches 0. This can be shown using the continuity of f, by choosing a suitable delta for ax that satisfies the given conditions. The example of f(x) = x^3 shows how the function can be stretched and the need to adapt the chosen delta accordingly.
  • #1
evry190
13
0
hey if lim (x-->0) f(x) = L

where 0 < |x| < d1 implies |f(x) - L | < e

how do i prove lim (x --> 0) f(ax) = L?

i know

0 < |ax| < |a|d1

d2 = |a|d1

but the textbook says d2 = d1/|a|

help you guyssssssssssssssssssssssssssssssss
 
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  • #2
You get to choose what d2 is
 
  • #3
You know that the function f is continuous, so you know that given epsilon > 0, there exists an delta > 0 satisfying
d(x)<delta -> d(f(x),l))<epsilon. Now your problem asks you to show that, given an epsilon > 0, you can find a delta such that d(x)<delta -> d(f(ax),l)<epsilon.

The point is that, you can also choose such a delta for ax. the continuity of the f immediately tells you that you can choose such a delta. What if f were the function f(x) = x^3? consider a neighborhood of f(x)=l=0, (-8,8). Then if x is between -2,2, we know that this relation holds. However, f(ax), a = 5, gives us a drastically stretched function. (-8, 8) is stretched to (-40, 40). if x is between -2/5, 2/5 = original delta/a, then d (f(ax), l) < d(f(x),l)<epsilon, because d(x) is now less than the first delta (2) in this case (because f(ax), x<delta over a implies that x from our second delta neighborhood, times a, is in our first delta neighborhood Adapt, and you'll be done.
 

1. What is the definition of a limit in calculus?

A limit in calculus is the value that a function approaches as its input approaches a certain value. It can be thought of as the value that the function "gets closer and closer to" as the input gets closer and closer to a specific value.

2. How is a limit typically written in mathematical notation?

A limit is typically written in mathematical notation as limx→a f(x) = L, where x represents the input, a represents the specific value the input is approaching, f(x) represents the function, and L represents the limit value.

3. What is the purpose of proving the limit of f(ax) with Delta Epsilon?

The purpose of proving the limit of f(ax) with Delta Epsilon is to show that a function has a specific limit value when its input approaches a certain value multiplied by a constant. This is helpful in understanding the behavior of functions and making predictions about their values.

4. What is Delta Epsilon and how is it used in proving limits?

Delta Epsilon is a mathematical concept used to prove limits. It represents the distance between the input value and the limit value. In a proof, it is used to show that for any arbitrarily small distance (epsilon), there exists a corresponding distance (delta) that ensures the function's output will be within epsilon of the limit value for all inputs within delta of the specific value.

5. What are the steps involved in proving the limit of f(ax) with Delta Epsilon?

The steps involved in proving the limit of f(ax) with Delta Epsilon are:
1. Start by writing out the definition of a limit in mathematical notation.
2. Manipulate the expression to find an equivalent expression that will be useful for the proof.
3. Set up the Delta Epsilon definition by replacing the limit value with L and the input value with a.
4. Use algebraic manipulation to find a suitable expression for delta in terms of epsilon and a.
5. Choose a value for delta that satisfies the expression found in the previous step.
6. Show that for any arbitrary epsilon, there exists a corresponding delta that satisfies the expression and proves the limit value.

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