Roots of the algebraic equation $${x^3} + {x^2} + x + 1 = 0$$ are

The function $$f\left( x \right) = 2x - {x^2} + 3\,\,$$ has

At $$t=0,$$ the function $$f\left( t \right) = {{\sin t} \over t}\,\,$$ has

Consider the function $$f\left( x \right) = {\left( {{x^2} - 4} \right)^2}$$ where $$x$$ is a real number. Then the function has