Consider the quadratic function $\displaystyle {f{{\left({x}\right)}}}=-{x}^{{2}}-{1}{x}+{20}$.

Determine the following: (enter all numerical answers as integers, fractions, or decimals):

The smallest $\displaystyle {x}$-intercept is $\displaystyle {x}=$ .
The largest $\displaystyle {x}$-intercept is $\displaystyle {x}=$ .
The $\displaystyle {y}$-intercept is $\displaystyle {y}=$ .
The vertex is ( , ).
The line of symmetry has the equation .