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Learn to estimate limit values by examining tables of function values
Learn step-by-step with practice exercises built right in.
One of the most intuitive ways to understand limits is by creating a table of values and observing the pattern.
To estimate :
Use a table to estimate . Check values from both sides.
| Section | Format | Questions | Time | Weight | Calculator |
|---|---|---|---|---|---|
| Multiple Choice (No Calculator) | MCQ | 30 | 60 min | 33.3% | ๐ซ |
| Multiple Choice (Calculator) | MCQ | 15 | 45 min | 16.7% | โ |
| Free Response (Calculator) | FRQ | 2 | 30 min | 16.7% | โ |
| Free Response (No Calculator) | FRQ | 4 | 60 min | 33.3% | ๐ซ |
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Let's find using a table.
Note: We can't just plug in x = 2 because we'd get (undefined!)
From the left (x < 2):
| x | f(x) = |
|---|---|
| 1.9 | |
| 1.99 | |
| 1.999 |
From the right (x > 2):
| x | f(x) = |
|---|---|
| 2.1 | |
| 2.01 | |
| 2.001 |
Both sides are approaching 4!
Therefore:
Tables are estimates! They might be misleading if:
Tables are excellent for building intuition, but algebraic methods (coming in later lessons) are more precise.
Let's create a table approaching x = 1:
From the left (x < 1):
| x | Decimal | |
|---|---|---|
| 0.9 | 0.526 | |
| 0.99 |
From the right (x > 1):
| x | Decimal | |
|---|---|---|
| 1.1 |
Both sides approach 0.5, so:
Estimate lim(xโ2) f(x) from the table: x: 1.9 1.99 1.999 2.001 2.01 2.1 f(x): 3.8 3.98 3.998 4.002 4.02 4.2
Step 1: Examine values as x approaches 2 from the left: x: 1.9 โ 1.99 โ 1.999 โ 2 f(x): 3.8 โ 3.98 โ 3.998 โ ? Values approach 4
Step 2: Examine values as x approaches 2 from the right: x: 2 โ 2.001 โ 2.01 โ 2.1 f(x): ? โ 4.002 โ 4.02 โ 4.2 Values approach 4
Step 3: Check agreement: Left-hand limit โ 4 Right-hand limit โ 4 Both agree!
Step 4: Conclusion: lim(xโ2) f(x) = 4
Answer: 4
Estimate lim(xโ0) (sin(x)/x) from the table: x: 0.1 0.01 0.001 -0.001 -0.01 -0.1 f(x): 0.9983 0.99998 0.999999 0.999999 0.99998 0.9983
Step 1: Examine from the right (positive x): x: 0.1 โ 0.01 โ 0.001 โ 0 f(x): 0.9983 โ 0.99998 โ 0.999999 โ ? Approaching 1
Step 2: Examine from the left (negative x): x: -0.1 โ -0.01 โ -0.001 โ 0 f(x): 0.9983 โ 0.99998 โ 0.999999 โ ? Also approaching 1
Step 3: Verify symmetry: Function values are the same from both sides Both approach 1
Step 4: Estimate the limit: lim(xโ0) (sin(x)/x) โ 1
Step 5: Note: This is a famous limit in calculus! Exact value is 1
Answer: 1
Use a table to estimate lim(xโ1) (xยณ - 1)/(x - 1)
Step 1: Create a table approaching from the left: x: 0.9 0.99 0.999 xยณ-1: -0.271 -0.0299 -0.003 x-1: -0.1 -0.01 -0.001 f(x): 2.71 2.9701 2.997
Step 2: Create a table approaching from the right: x: 1.1 1.01 1.001 xยณ-1: 0.331 0.0303 0.003 x-1: 0.1 0.01 0.001 f(x): 3.31 3.0301 3.003
Step 3: Analyze the pattern: From left: 2.71 โ 2.9701 โ 2.997 โ ? From right: 3.31 โ 3.0301 โ 3.003 โ ? Both approaching 3
Step 4: Estimate: lim(xโ1) (xยณ - 1)/(x - 1) โ 3
Step 5: Verification (algebraic): xยณ - 1 = (x - 1)(xยฒ + x + 1) (xยณ - 1)/(x - 1) = xยฒ + x + 1 At x = 1: 1 + 1 + 1 = 3 โ
Answer: 3
Estimate lim(xโ0โบ) (1/x) from the table. What happens? x: 0.1 0.01 0.001 0.0001 f(x): 10 100 1000 10000
Step 1: Examine the pattern: As x gets smaller (closer to 0): x: 0.1 โ 0.01 โ 0.001 โ 0.0001 โ 0โบ f(x): 10 โ 100 โ 1000 โ 10000 โ ?
Step 2: Observe the behavior: The function values are growing without bound They're increasing toward infinity
Step 3: Conclusion: The limit does not exist as a finite number We say: lim(xโ0โบ) (1/x) = โ
Step 4: Important note: This is an "infinite limit" โ is not a number, it describes unbounded growth
Step 5: Graphical interpretation: The graph has a vertical asymptote at x = 0
Answer: The limit is โ (infinite limit)
| 0.503 |
| 0.999 | 0.500 |
| 0.476 |
| 1.01 | 0.498 |
| 1.001 | 0.500 |