Free graphing resources · Original practice
Graphing exponential functions.
Read the ratio in the curve.
Plot four original exponential functions from y=a·b^(x-h)+k. Compare growth, decay, horizontal shifts and vertical offsets using listed sample points.
4 exponential cases.
Growth, decay and shifts.
More ways to practice
Read the graph before you write the rule
A reliable way to practice is to start from a drawn curve and recover a possible equation of the form y = a·b^(x-h) + k, where b > 0 and b ≠ 1. The horizontal asymptote gives k directly: if the curve flattens toward y = 2, then k = 2. The horizontal shift h is the x-value where the exponential part equals 1, so the point (h, a + k) sits one vertical step of size a above the asymptote.
Choose two clear points to solve for a and b. Substitute both into y = a·b^(x-h) + k and divide one equation by the other to eliminate a. If the resulting ratio is positive, b is positive; if it is not, your chosen points or assumed h are inconsistent. This backward reading is a strong check because it forces every parameter to earn its place.
- Mark the horizontal asymptote and record k.
- Identify the point where the curve is exactly a units above the asymptote; its x-value is h.
- Pick two well-separated points with readable coordinates.
- Substitute both points, divide to find b, then solve for a.
- Test a third point that you did not use in the calculation.
A fresh worked variation with a negative leading coefficient
Most introductory examples use a positive a, so the curve rises above its asymptote on one side. A negative a reflects the curve below the asymptote. For y = -2·3^(x-1) + 4, the asymptote is y = 4, and because a = -2 the graph approaches 4 from below as x decreases. At x = 1 the exponential part is 1, giving y = 2, so the point (1, 2) is two units below the asymptote.
Check the direction with two more inputs. At x = 0, y = -2·3^(-1) + 4 = -2/3 + 4 = 10/3, about 3.33. At x = 2, y = -2·3 + 4 = -2. The values move from about 3.33 down through 2 to -2, confirming a decreasing curve that flattens toward 4 on the left and falls away on the right. The domain is all real x; the range is y < 4 because the curve never reaches the asymptote.
- Write the asymptote as a dashed horizontal line before plotting.
- Compute the anchor point at x = h and mark it.
- Compute one point on each side of h using simple integer inputs.
- Draw a smooth curve that approaches but does not cross the asymptote.
- State domain and range explicitly, using an open inequality for the asymptote.
Diagnostic checks that separate plotting from solving
A blank coordinate grid is not an answer. The graph must show the asymptote, at least three labeled points, and arrowheads or clear end behavior. Check the y-intercept by substituting x = 0, not by guessing from the drawing. Check whether the curve crosses the asymptote: for a pure exponential with a ≠ 0, it should not. If your drawn curve crosses, either the asymptote is misplaced or a plotted point is wrong.
Endpoint questions matter when a task restricts the domain, for example x ≥ 0. Then the graph is a ray-like segment starting at a solid or open endpoint depending on the inequality. Substitute the endpoint value to place it, and mark open endpoints with a hollow circle. For unrestricted exponential graphs, the domain is all real numbers and there is no endpoint to close.
- Substitute x = 0 to verify the y-intercept.
- Confirm the curve never touches the asymptote.
- Check one point left of h and one right of h.
- If the domain is restricted, mark the endpoint as open or closed according to the inequality.
- Compare the steepness with b: larger b gives faster growth for x > h.
Try this example
A curve has horizontal asymptote y = 1, passes through (0, 3) and (2, 7), and is assumed to have the form y = a·2^x + 1. Verify whether these points fit and state the range.
Show the worked explanation
At x = 0: a·2^0 + 1 = a + 1 = 3, so a = 2. At x = 2: 2·2^2 + 1 = 8 + 1 = 9, not 7. The assumed base 2 does not fit both points. Using y = a·b^x + 1 with (0, 3) gives a = 2. Then 2·b^2 + 1 = 7 gives b^2 = 3, so b = √3. The rule is y = 2·(√3)^x + 1. Since a = 2 > 0, the range is y > 1, and the asymptote y = 1 is never reached.
Common mistakes
- Treating the asymptote as an axis and plotting points relative to y = 0. Draw and label the asymptote first, then measure vertical distances from that line when locating the anchor point.
- Assuming a negative leading coefficient means the function is undefined or has no range. Remember a negative a reflects the curve below the asymptote; state the range as y < k when a < 0.
- Drawing a curve that crosses the horizontal asymptote to connect distant points. Keep the curve on one side of the asymptote and let it flatten; recheck any point that would force a crossing.
Check your work
- The horizontal asymptote is drawn and labeled with its equation.
- At least three plotted points are labeled with coordinates.
- The anchor point at x = h is correctly placed relative to the asymptote.
- The curve approaches but does not cross the asymptote.
- Domain and range are stated with correct inequality direction.
- Any restricted-domain endpoint is marked open or closed correctly.
Questions before you start
How do I find the horizontal shift from a graph?
Locate the point where the curve is exactly a units above or below the asymptote. Its x-coordinate is h in y = a·b^(x-h) + k.
Can an exponential graph have a y-intercept of zero?
Only in special shifted cases. Substitute x = 0 into the rule to check; do not assume the intercept from the asymptote alone.
What changes when the domain is restricted?
The curve becomes a segment with an endpoint. Substitute the boundary x-value to place it, and use an open or closed circle according to the inequality.