5. Limits of Functions

Calculus 1



Weiqi Zhou

Motivating Examples

Limits of Functions

we call the limit of as , if for any , there exists some , so that holds for all in

Limits of Functions

is the limit of as ,if converges to for any with (for all ) that converges to

Limits of Functions

to have a limit at , need not be defined at
but shall be defined near

Example

  • show that

  • for any , take

  • if ,then holds for all in

  • if ,then also holds for all in

Example

  • show that does not have a limit as

  • take any positive sequence that converges to ,then converges to as it is a constant sequence

  • take any negative sequence that converges to ,then converges to

Exercise

show that does not have a limit as

One-sided Limit

the limit as approach from one side (i.e., from left or from right)

Left Limit

is the left limit of as , if for any , there exists some , so that holds for all in

Left Limit

is the left limit of as ,if converges to for any with (for all ) that converges to

Right Limit

is the right limit of as , if for any , there exists some , so that holds for all in

Right Limit

is the right limit of as ,if converges to for any with (for all ) that converges to

Notations

: is the left limit of as

: is the right limit of as

Examples

  • show that does not have a limit as



Exercise

compute the left limit and the right limit of

as respectively

Limit as

is the limit of as , if for any , there exists some , so that holds for all in

Limits as

it is also viable to define as

Exercise

Show that

Properties

  • if the limit of is as ,then it is unique and

  • is bounded near : there exists ,so that holds for all in

  • is close to near : there exists ,so that (if ) holds for any in

Two Important Cases

Exercises

Summary

  • Limits of Functions

  • One-sided Limits

  • Properties

  • Two Important Cases