how can we display our real roots or points

>> f = @(x) x^3-3*x-1;
>> fplot(f, [-10 10]); grid on;

[Andrew Newell]

Do you want to find the roots or just change the display so you can see the crossings?

[adriana resendez]

both

Answer 1

[Star Strider]

Use the roots function:

xr = roots([1 0 -3 -1]);

They all happen to be real. This gives the x-values, so if you want to plot them, the y vector is:

yr = zeros(size(xr));

[Andrew Newell]

To make the roots visible on the plot, use

set(gca,'YLim',[-10 10])

[adriana resendez]

did you mean size 'r' i dont have a defined variable for r

[adriana resendez]

on the m file?

[Star Strider]

I changed ‘r’ to ‘xr’ when I created ‘yr’ and forgot to change it in ‘yr’. The code is consistent now.

With a couple tweaks, you can plot everything easily:

f = @(x) x^3-3*x-1;
xr = roots([1 0 -3 -1]);
yr = zeros(size(xr));

figure(1)
fplot(f, [-10 10], '-r')
hold on
plot(xr, yr, 'bp')
hold off
grid on