OpenOffice is an officesoftware suite that can be downloaded for free. OpenOffice includes a word processor, spreadsheets and presentation software. The spreadsheet feature can be used to input data and plot the data on a graph. OpenOffice will calculate the slope between two points on a graphed line and the yintercept of a graph when the user inputs an equation.

Locate the portion of the line graph for which you want to calculate the slope. Locate the point at the top of the line segment and the point at the bottom of the line segment. The slope of one line can be different if the line is not completely straight. You have to choose a segment of the line for calculating slope accurately. To calculate the yintercept, you only need two points on a line.

Open OpenOffice Calc and enter the following formula into any cell on the spreadsheet:
=SLOPE(yvalues,xvalues).
In the place of "yvalues" and "xvalues," enter the ycoordinates of your two points separated by a semicolon. For example, =SLOPE(B4:B10, A5:A8).
Enter the following formula in a cell above or below the row you used to calculate slope:
=INTERCEPT(yvalues,xvalues).
You can enter the same two x and ycoordinates you used to calculate slope.

Press "Enter" to calculate the slope and yintercept. The answer will be displayed in a box to the left of the formula you entered.
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