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Section 1 · Module 1.1 · Topic 2

Limits

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TimeCells
1:00 PM1,000
2:00 PM1,200
3:00 PM1,400
4:00 PM1,600
5:00 PM1,800
6:00 PM2,000
7:00 PM2,200
Average growth rate=200cells / hour

But what was the growth rate at exactly 1:37 PM?

We can't measure at a single instant — but we can shrink the interval around it and see what happens.

Magnification

Field view — multiple bacteria visible

Does the bacterium change
when magnification increases?

y = x² near x = 2

Use the zoom slider to investigate what happens to y as x approaches 2.

024-1001020y = x²
Zoom1×

Low zoom — parabola looks broad and curved

A Weird Case

What if the function has a hole?

At x = 1 this function is undefined. Can a limit still exist?

02024undefinedy = (x²−1)/(x−1)
Approach x = 1δ = 1.4

Move the slider to approach x = 1 from both sides

Formal Notation

limx → a
f(x)

What value does f(x) approach as x approaches a?

What does a limit describe?

Question

Can a limit exist even if a function is not defined at that point?

tap to reveal →

Answer

Yes. The limit only cares about values near that point — not at it.

← tap to flip back

Question

Why do we use limits?

tap to reveal →

Answer

To understand behavior at extremely small scales.

← tap to flip back

Imagine measuring growth rate
over smaller and smaller time intervals.

Which mathematical idea allows us to talk about growth at a single instant?

A value tells you where you are.

A limit tells you where you are heading.

What's Coming Next

What if zooming from the left
and zooming from the right
tell different stories?

01234135→ 3→ 5gap
Left side approaches 3
Right side approaches 5

Next concept is what happens

When Limits Fail

(Continuity)

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