+15 Let a, b, c, and d be distinct real numbers such that
\( \begin{align*} a &= \sqrt{4 + \sqrt{5 + a}}, \\ b &= \sqrt{4 - \sqrt{5 + b}}, \\ c &= \sqrt{4 + \sqrt{5 - c}}, \\ d &= \sqrt{4 - \sqrt{5 - d}}. \end{align*}\)
Compute abcd.
+159 Please convert the latex code to an image, or write it out in english.
