Determining the gradient of a line. (1 Viewer)

[nofate]

If there is a question that says, using the graph, determine the slope of the line, is the following way acceptable?

The line starts at (0,0) and finishes at roughly (1, 1.6). You know it passes through exactly at (0.4, 0.6). Can you do m = 0.6/0.4?

My teacher advises us to use the full line in our working, i.e. m = (1.6 - 0)/(1-0). However, as in this example, the end point isn't always that easy to determine, and therefore it would lead to an inaccurate calculation. Thus is the former way acceptable by HSC markers?

Thanks

 

[deswa1]

Its the gradient of a straight line lol- its constant no matter which two points you pick. What you must make sure you do though is pick two points ON the line of best fit- not neccessarily two points from your data because they might not lie exactly on the line of best fit.

In your case, if the line of best fit passed through (0,0) and (0.4, 0.6), then you go:
m=(0.6-0)/(0.4-0) etc.

Remember to put the -0 on the top and bottom so the marker can see where you are taking the second point as