\[\boxed{\mathbf{68.}}\]
\[Верхняя\ полуокружность\ \]
\[радиуса\ R:\]
\[y = \sqrt{R^{2} - x^{2}}.\]
\[\textbf{а)}\ y = \sqrt{4 - x^{2}}\]
\[\textbf{б)}\ y = - \sqrt{4 - x^{2}}\]
\[\textbf{в)}\ y = \sqrt{9 - (x - 1)^{2}}\]
\[\textbf{г)}\ y = - \sqrt{9 - (x + 1)^{2}}\]
\[\textbf{д)}\ y = \sqrt{16 - (x + 2)^{2}} - 2\]
\[\textbf{е)}\ y = - \sqrt{25 - (x - 3)^{2}} + 1\]