Eric Weisstein's World of Mathematics, <a href="httphttps://mathworld.wolfram.com/ReflectionTriangle.html">Reflection Triangle</a>.
Eric Weisstein's World of Mathematics, <a href="httphttps://mathworld.wolfram.com/SquareRoot.html">Square Root</a>.
Eric Weisstein's World of Mathematics, <a href="httphttps://mathworld.wolfram.com/TheodorussConstant.html">Theodorus's Constant</a>.