1.For first expression you should do like in the next example:
int n = 10;
StringBuilder builder = new StringBuilder();
double resultValue = 0;
double temp = 1;
for (int i = 0; i < n; i++)
{
if (i > 0)
builder.Append(" + ");
builder.Append(string.Format("{0}!", i + 1));
temp *= (i + 1);
resultValue += temp;
}
builder.Append(string.Format(" = {0}", resultValue));
_textBox.Text = builder.ToString();
2.For 2nd expression a similar code like below:
int n = 10;
StringBuilder builder = new StringBuilder();
double resultValue = 0;
double temp = 1;
for (int i = 0; i < n; i++)
{
if (i > 0)
builder.Append(" + ");
builder.Append(string.Format("1/{0}!", i + 1));
temp *= (i + 1);
resultValue += 1/temp;
}
builder.Append(string.Format(" = {0}", Math.Round(resultValue, 2)));
_textBox.Text = builder.ToString();