The viewing window is your frame: The GDC graph is only as good as the window you choose. A bad window hides the key features — intercepts, turning points, asymptotes — that IB questions ask about. Getting the window right is a skill, not an afterthought.
The four settings you control are Xmin, Xmax, Ymin and Ymax. Together they define the rectangle of the coordinate plane that appears on screen.
| Setting | What it controls | Typical starting value |
|---|---|---|
| Xmin | Left edge of the x-axis | −10 (or 0 for time/distance) |
| Xmax | Right edge of the x-axis | 10 (adjust for context) |
| Ymin | Bottom edge of the y-axis | −10 (or 0 for positive quantities) |
| Ymax | Top edge of the y-axis | 10 (or higher for cost/population) |
| Xscl / Yscl | Tick-mark spacing | 1 or 2 (cosmetic only) |
Start with ZoomStd or ZoomFit, then adjust: On a TI-84: press ZOOM → 6 (ZStandard) for a −10 to 10 window, or ZOOM → 0 (ZoomFit) to auto-scale. On a Casio fx-CG50: press SHIFT+F3 (V-Window) and type values manually. Then zoom in on the interesting part.
x-intercept = zero; intersection = two curves meeting: The x-intercept of f(x) is where f(x) = 0 — the curve crosses the x-axis. An intersection point is where two different functions are equal: f(x) = g(x).
The cost of hiring a bicycle is C(d) = 60d + 10 for d ≥ 3. A competitor charges G(d) = 50d + 40. Find the number of days for which both companies charge the same amount.
Step by step
- Enter both functions in Y1 and Y2 on the GDC.
- Set a window that captures the intersection. Since d ≥ 3, use Xmin = 0, Xmax = 10, Ymin = 0, Ymax = 700.
- Use Calc → Intersect (TI: 2nd TRACE 5; Casio: G-Solv → ISCT).
- Read the intersection coordinates.
Final answer
After 3 days both companies charge $190.
Always check the domain: The GDC finds all mathematical intersections. But if the model only applies for d ≥ 3 (as above), reject any intersection at d < 3. The GDC does not know about domain restrictions — you do.
Study smarter, not longer
Most students waste 40% of study time on topics they already know. Our AI tracks your progress and optimizes every minute.
Local max/min = the peak or trough on the visible curve: The GDC can locate turning points numerically. You do not need calculus — just the right menu. On TI: 2nd TRACE → Maximum or Minimum. On Casio: G-Solv → MAX or MIN.
A dolphin's height (metres) during a jump is h(d) = −0.5d² + 3d, where d is horizontal distance. Find the maximum height and the horizontal distance at which it occurs.
Step by step
- Enter h(d) = −0.5x² + 3x in Y1.
- Choose a window: Xmin = 0, Xmax = 7, Ymin = −1, Ymax = 6.
- Use Calc → Maximum. Move left bound to x = 0, right bound to x = 6, guess near the peak.
- GDC returns the maximum point.
Final answer
Maximum height = 4.5 m at horizontal distance d = 3 m.
State coordinates, not just the y-value: IB mark schemes usually want both the x-coordinate (where the max occurs) and the y-coordinate (the maximum value). Write: "Maximum at (3, 4.5)" — not just "4.5 metres".
The GDC gives numbers — you give meaning: Every coordinate the GDC returns must be interpreted in the context of the problem. "x = 3" means nothing on its own; "after 3 days" or "at distance 3 metres" is the answer.
✗ Incomplete answer
- x = 3, y = 190
- Maximum = 4.5
- Intersection at x = 6
✓ Full IB answer
- After 3 days, both companies charge $190.
- The maximum height of the dolphin is 4.5 m, occurring at a horizontal distance of 3 m.
- The two functions are equal when x = 6 hours; revenue = $540.
Round appropriately: IB questions say "give your answer correct to ... decimal places" or "to the nearest integer". If no rounding instruction is given, 3 significant figures is standard. Never give a 10-digit GDC readout as your answer.
GDC output checklist
- Did you set a window that captures ALL key features?
- Did you use the correct menu (zero / intersect / max / min)?
- Did you interpret the coordinate using the units from the question?
- Did you check whether the answer is within the domain?
- Did you round to the precision asked for?