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

  • Thread starter Thread starter gottfried
  • Start date Start date
  • Tags Tags
    Continuous
Click For Summary
SUMMARY

The discussion focuses on proving the continuity of the function f(x) = 2x² + 5 at x = 3 using the formal definition of continuity. The key steps involve demonstrating that for every ε > 0, there exists a δ > 0 such that |x - 3| < δ implies |2x² + 5 - 23| < ε. The participants emphasize the importance of manipulating the expression |2(x² - 9)| and applying the triangle inequality to establish the relationship between δ and ε effectively.

PREREQUISITES
  • Understanding of the formal definition of continuity in calculus
  • Familiarity with the triangle inequality theorem
  • Basic algebraic manipulation of polynomial expressions
  • Knowledge of limits and ε-δ proofs
NEXT STEPS
  • Study the formal definition of continuity in calculus
  • Learn how to apply the triangle inequality in proofs
  • Practice ε-δ proofs with various functions
  • Explore polynomial functions and their continuity properties
USEFUL FOR

Students studying calculus, particularly those focusing on continuity and limits, as well as educators looking for examples of ε-δ proofs in action.

gottfried
Messages
118
Reaction score
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
hi gottfried! :smile:

if eg you insist that δ < 1, then |x+3| is between 5 and 7 :wink:
 
|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.
 

Similar threads

Replies
7
Views
2K
Replies
30
Views
3K
  • · Replies 8 ·
Replies
8
Views
2K
Replies
4
Views
4K
  • · Replies 22 ·
Replies
22
Views
4K
  • · Replies 12 ·
Replies
12
Views
2K
  • · Replies 2 ·
Replies
2
Views
3K
  • · Replies 4 ·
Replies
4
Views
1K
  • · Replies 5 ·
Replies
5
Views
2K
  • · Replies 23 ·
Replies
23
Views
3K