LESSON 1 · 16 MIN
Graphical analysis
Read axes, units, scale, points, slope, intercept, and domain, then test whether a table, equation, and graph encode the same relation.
ESSENTIAL QUESTIONWhich marks are observations, which values are modeled between them, and where does the stated domain stop?
Axes, points, connection rule, and domain travel together.
Open the complete data table
| Series | Point | Time (h) | Distance (mi) |
|---|---|---|---|
| Measured points with stated straight segments | Start | 0 | 0 |
| Measured points with stated straight segments | Two-hour observation | 2 | 100 |
| Measured points with stated straight segments | Four-hour observation | 4 | 200 |
Open the complete data table
| Series | Point | Time (min) | Volume (mL) |
|---|---|---|---|
| Measured points with stated straight segments | Start | 0 | 0 |
| Measured points with stated straight segments | Two-minute observation | 2 | 24 |
| Measured points with stated straight segments | Five-minute observation | 5 | 60 |
Open the complete data table
| Series | Point | Input (x-units) | Output (y-units) |
|---|---|---|---|
| Measured points with stated straight segments | Intercept | 0 | 4 |
| Measured points with stated straight segments | Middle observation | 2 | 10 |
| Measured points with stated straight segments | Domain endpoint | 4 | 16 |
| Graph | x-axis contract | y-axis contract | Connection rule | Stated domain |
|---|---|---|---|---|
| Distance traveled over four hours | Time: 0–4 h; tick 1 h | Distance: 0–200 mi; tick 50 mi | Straight segments between adjacent source points | 0 ≤ time ≤ 4 h |
| Collected volume over five minutes | Time: 0–5 min; tick 1 min | Volume: 0–60 mL; tick 12 mL | Straight segments between adjacent source points | 0 ≤ time ≤ 5 min |
| Equivalent linear representations | Input: 0–4 x-units; tick 1 x-units | Output: 0–16 y-units; tick 4 y-units | Straight segments between adjacent source points | 0 ≤ input ≤ 4 x-units |
Read the contract
Name both variables, units, axis ranges, tick intervals, series encoding, source points, and stated domain before calculating.
- Tick spacing—not visual distance alone—sets scale.
- The source table is the complete nonvisual equivalent.
Separate point types
Observed points come from the source data; interpolation uses an explicit between-point model; extrapolation leaves the stated domain.
- A connected segment authorizes only the stated in-domain interpretation.
- Never continue a trend past an endpoint without an explicit model.
Match invariants
Equivalent equations, tables, and graphs must agree on intercept, slope or shape, values, and allowed inputs.
- Slope carries output-units per input-unit.
- A matching equation with a different domain is a different model.
Worked example
A straight-segment graph contains (0 h, 0 mi), (2 h, 100 mi), and (4 h, 200 mi). What does it show at 3 h, and what may it claim at 5 h?
- 1
The axes identify time in hours and distance in miles; the stated domain is 0 through 4 hours.
- 2
Three hours lies between the 2-hour and 4-hour observations, so the stated straight segment gives 150 miles.
- 3
Five hours lies beyond the stated domain, so 250 miles would be an unsupported extrapolation unless another model is supplied.
ConclusionThe graph supports 150 miles at 3 hours by interpolation and supports no value at 5 hours under the given contract.
Calculator decision ledger
- Model mentally
- Read axis labels, units, source points, connection rule, and domain before keying values.
- Estimate
- Predict direction, intercept, and approximate change per input unit from the complete table.
- Calculator
- Use division only when the exact change ratio is not immediate from the supplied values.
- Audit
- Reattach slope units and classify the input as observed, interpolated, or beyond the domain.
Close the notes first
Retrieve the model.
01What must be read before comparing two drawn slopes?
Drawing angle changes when an axis scale changes; slope is an exact change ratio with units.
02How does interpolation differ from extrapolation?
The evidence boundary is set by the source points, connection rule, and stated domain.
03Why can two equations that share points still represent different models?
A few shared values do not establish agreement over every permitted input.