input equation from text box

[C# Programming]

HI http://www.barakasoft.com/script/Forums/Images/smiley_cool.gif
when i want to input my equation (ex: ((Math.Pow(x,5)) + x - 1) ) from textbox to function this erro
appear . format exeption was unhandeld .

my code is here


public double func(double x)
{
return (double.Parse((txtEq.Text)));
}



i want to user can input equation from textbox.

Thank u so much http://www.barakasoft.com/script/Forums/Images/smiley_smile.gif