Getting an equation from a graph

  • Thread starter Neal Johnson
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In summary, to get equations for nonlinear graphs using a graphing calculator, use the STAT function and choose CALC. Excel also offers a trend line option, but lacks a trigonometric option.
  • #1
Neal Johnson
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I have fairly simple non linear graphs that I need equations for. Sometime back I used a program that gave me a power series equation when multiple cordinates of the graph were entered. I no longer have that program and don't remember where I got it. How Can I get these equations? There must be a procedure I can follow.
 
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  • #2
I don't know about a specific method unless you know the degree of the polynomial?
 
  • #4
On a good graphing calculator, use the STAT function and choose CALC. Assuming you've already entered a table of data, it gives you several options: linear regression, logarithmic regression, exponential, power (to several orders), trigonometric (fitting a sine curve to the data), etc. I'd have to look at the manual to remember the details of the process, but the result is an equation that will recreate the same pattern.

I usually use Excel, since it's on just about every computer and spreadsheets are almost always more functional than entering data into a calculator.

In Excel, once you've plotted your data, you can add a trend line. The options for the trend line are similar to the options on a graphing calculator, with the advantage that as you select each option, you can immediately see how well the trend line matches the plotted data. The disadvantage is that Excel doesn't offer a trigonometric option, a major drawback. You can come close using a higher order polynomial, but it's not as good. (On the other hand, if you've taken basic trigonometry, it's really fairly easy to fit a sine wave to your data, when appropriate, even without the aid of a computer or calculator.) When you have a trend line that comes close to matching your data, select the option to display the equation on the chart.

Just looking at the plotted data should give you a decent clue of the type of equation that would model it best, so you usually only have to try a couple of options regardless of whether you're using a calculator or Excel.
 
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  • #5
There once was something downloadable called, CurveExpert, but not sure if it is still available.
 

1. How do I find the equation of a line from a graph?

To find the equation of a line from a graph, you need to know the slope and the y-intercept of the line. The slope can be calculated by finding the change in y values over the change in x values, while the y-intercept is the y value where the line crosses the y-axis. Once you have these values, you can use the slope-intercept form of a line (y = mx + b) to write the equation.

2. What is the slope-intercept form of a line?

The slope-intercept form of a line is y = mx + b, where m is the slope of the line and b is the y-intercept. This form allows you to easily identify the slope and y-intercept of a line and write its equation.

3. Can I use any two points on the line to find the equation?

Yes, you can use any two points on a line to find the equation. You can calculate the slope using the coordinates of these two points, and then use one of the points to find the y-intercept. However, it is usually easier to find the equation if you use the y-intercept and another point on the line.

4. How do I determine the slope and y-intercept from a graph?

To determine the slope and y-intercept from a graph, you can visually identify two points on the line and use the slope formula (m = (y2 - y1) / (x2 - x1)) to calculate the slope. Then, you can use one of the points to find the y-intercept by plugging in its coordinates into the slope-intercept form of a line (y = mx + b).

5. Can I use the equation to find other points on the line?

Yes, you can use the equation to find other points on the line. Simply plug in different values for x into the equation and solve for y. The resulting ordered pairs (x, y) will be points on the line.

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