“Why Can’t I see the graph”
Sometimes you want to see the graph of a function – but when punch it in the CAS Calculator the graph doesn’t appear.
You can’t see it.
Here’s an example f(x)=1000(90-x)^3
This usually happens when you’re given functions that use large numbers – specifically when you’re dilating by a large number…
and if you can see graph, its probably just a straight line.
This can throw many students off track.
For our example f(x) is a cubic function dilated by a factor of 1000 from the x-axis.
Sketching this you initially can’t see the graph on your CAS and if/when you do find it – 10X zooming out its just a straight line…
and your thinking “this ain’t right”.
Here’s what you need to do:
1) Ignore the large dilating factor and see if you can identify the shape of the graph.
For f(x) ignoring the 1000 we can see that f(x) is a cubic function written in turning point form.
The cubic function is translated 90 units to the right…
and so the shape of this function f(x) should be a basic cubic function translated 90 units to the right, and stretched vertically by a dilation of 1000.
Change the window settings on you CAS so you can clearly see the x-axis intercepts at x=90.
Hint: make the axis start at x=88 and end at x=92.
You should be able to clearly see the shape of this graph now.
2) If you can identify the shape or known key features of the graph eg asymptotes, turning points or axis intercepts – then try changing your CAS windows settings around these areas so you can get a better view of the graph.
Usually zooming in/out and moving axis to left or right works.
But if it doesn’t work and your fortunate enough not to be sitting an exam or sac during this time then try…
3) Desmos Graphing Calculator online. This is a great tool you can use to visualise graphs and a lot easier to use compared to your CAS calculator.
Zooming in/out and moving the axis is simple allowing you to quickly find the shape of the graph.