\[\boxed{\text{89.\ }\text{ОК\ ГДЗ\ -\ домашка\ на\ 5}}\]
\[\textbf{а)}\ x = 7 - 2\sqrt{15} =\]
\[= \sqrt{49} - \sqrt{60} < 0\]
\[|x| = - x.\]
\[\textbf{б)}\ x = 2\sqrt{13} - 7 =\]
\[= \sqrt{52} - \sqrt{49} > 0\]
\[|x| = x.\]