Finding Derivatives Implicitly and Explicitly In Exercises $21-24,$ (a) find two explicit functions by solving the equation for $y$ in terms of $x,($ b) sketch the graph of the equation and label the parts differentiate the explicit functions, and (d) find $d y / d x$ implicitly and show that the result is equivalent to that of part (c).
$$
x^{2}+y^{2}=64
$$