Relative Minimum
Press 
to access the minimum option
which finds a value of a variable in the interval between a lower and
upper bound that minimizes the expression.
Next, enter an expression, the variable, a lower bound, and an upper bound
separated by commas. For example, to find the minimum value
of the expression x - x3 for x between -1 and 1 enter
3
1
1 
The minimum value is about -0.577.