Prove 2x^2+5 is continuous at x=3

  • Thread starter gottfried
  • Start date
  • Tags
    Continuous
In summary, a function is continuous at a point if the limit of the function as x approaches that point is equal to the value of the function at that point. To calculate the limit, the value of the point can be substituted into the function. To prove continuity at a specific point, the limit must be shown to be equal to the value of the function at that point. There are three types of discontinuities - removable, jump, and infinite - and not every continuous function is differentiable.
  • #1
gottfried
119
0

Homework Statement



Using the de finition of continuity show that f(x) = 2x2 + 5 is continuous at x = 3

Homework Equations





The Attempt at a Solution


For all ε>0 there exists δ>0 such that |x-3|<δ implies that |2x2 + 5 -23| = |2(x2-9)| = |2(x+3)(x-3)| < |2(x+3)δ|

Could anybody give me advice as to where I should take it from here to show that |2x2 + 5 -23|<ε
 
Physics news on Phys.org
  • #2
hi gottfried! :smile:

if eg you insist that δ < 1, then |x+3| is between 5 and 7 :wink:
 
  • #3
|2(x+3)(x-3)| = 2|x+3||x-3| < 2δ|x+3|

Now is |x+3| = |x - 3 + 6| ? Also remember to use the triangle inequality.
 

What does it mean for a function to be continuous at a point?

For a function to be continuous at a point, it means that the limit of the function as x approaches that point is equal to the value of the function at that point. In other words, there are no abrupt jumps or breaks in the graph of the function at that point.

What is the limit of 2x^2+5 as x approaches 3?

The limit of 2x^2+5 as x approaches 3 is 23. This can be calculated by substituting the value of 3 for x in the function and solving for the resulting expression, which is 23 in this case.

How can you prove that 2x^2+5 is continuous at x=3?

To prove that 2x^2+5 is continuous at x=3, you can use the definition of continuity and show that the limit of the function as x approaches 3 is equal to the value of the function at x=3. This can be done by substituting 3 for x in the function and showing that the resulting expression is equal to 23.

What are the different types of discontinuities?

There are three types of discontinuities - removable, jump, and infinite. A removable discontinuity occurs when there is a hole in the graph of the function at a particular point. A jump discontinuity occurs when there is a sudden jump or gap in the graph at a point. An infinite discontinuity occurs when the limit of the function at a point is either positive or negative infinity.

Is every continuous function differentiable?

No, not every continuous function is differentiable. A function is differentiable at a point if its derivative exists at that point. There are certain types of functions, such as those with corners or sharp turns, that are continuous but not differentiable at certain points. However, if a function is differentiable at a point, it must also be continuous at that point.

Similar threads

  • Calculus and Beyond Homework Help
Replies
30
Views
2K
  • Calculus and Beyond Homework Help
Replies
4
Views
2K
  • Calculus and Beyond Homework Help
Replies
8
Views
2K
  • Calculus and Beyond Homework Help
Replies
5
Views
1K
  • Calculus and Beyond Homework Help
Replies
22
Views
3K
  • Calculus and Beyond Homework Help
Replies
4
Views
562
  • Calculus and Beyond Homework Help
Replies
12
Views
2K
  • Calculus and Beyond Homework Help
Replies
3
Views
1K
  • Calculus and Beyond Homework Help
Replies
2
Views
2K
  • Calculus and Beyond Homework Help
Replies
5
Views
2K
Back
Top