Let a, b, c, and d be distinct real numbers such that $a = \sqrt{4 + \sqrt{5 + a}}, \\ b = \sqrt{4 - \sqrt{5 + b}}, \\ c = \sqrt{4 + \sqrt{5 - c}}, \\ d = \sqrt{4 - \sqrt{5 - d}}.$ Compute $abcd$.
I found it here!
https://web2.0calc.com/questions/let-a-b-c-and-d-be-distinct-real-numbers-such-that
+25 
