Symbolism is a C# library which implements automatic simplification of algebraic expressions.
Going with your example expression, the following program:
var x = new Symbol("x");
(5 * x * (500 / (x ^ 2) * (sqrt(3.0) / 4) + 1) + 2 * (x ^ 2) + (sqrt(3.0) / 2) * (x ^ 2))
.AlgebraicExpand()
.Disp();
displays this at the console:
1082.5317547305483 / x + 5 * x + 2.8660254037844384 * (x ^ 2)