Solve the initial-value problem for y\displaystyle {y} as a function of x\displaystyle {x}. (81x2)dydx=1\displaystyle {\left({81}-{x}^{{2}}\right)}\frac{{{\left.{d}{y}\right.}}}{{{\left.{d}{x}\right.}}}={1}, y(0)=4\displaystyle {y}{\left({0}\right)}={4}

y=\displaystyle {y}=