Consider the function $$y = \left| x \right|$$ in the interval $$\left[ { - 1,1} \right]$$. In this interval, the function is

The formula used to compute an approximation for the second derivative of a function $$f$$ at a point $${x_0}$$ is

$$\mathop {Lim}\limits_{x \to \infty } {{{x^3} - \cos x} \over {{x^2} + {{\left( {\sin x} \right)}^2}}} = \_\_\_\_\_\_.$$

If at every point of a certain curve, the slope of the tangent equals $${{ - 2x} \over y}$$ the curve is