I have an example of a function $f(x)=x^2+x$, this is specifically for an example explaining the dependency problem.
In it we are interested the values over the interval $[-1,1]$, with them being $[-\frac{1}{4},2]$
In the example we apply the interval in context of the function:
$[-1,1]^2+[-1,1]=[0,1]+[-1,1]=[-1,2]$
I want to know why, in the first step, $[-1,1]^2 = [0,1]$?
Apologies if the answer is trivial, this is not my strong point.