You could define an anonymous function f(x):
f = @(x) x.*(x.^2-1);
Note the '.' before the * and ^operators. This lets the function work with array inputs. I use this feature in the example at the end.
Now you can use cos(t) as an argument to f:
t = 2;
y = f(cos(t))
Or you may define a new anonymous function g:
g = @(t) f(cos(t));
You may now try something like this:
t = linspace(0,2*pi);
plot(t,g(t))
You may want to take a look at the Matlab documentation for anonymous functions.
