TDIST function

Returns the Student's t-distribution


 * TDIST(x,deg_freedom,tails)
 * X - the numeric value at which to evaluate the distribution.
 * Deg_freedom - an integer indicating the number of degrees of freedom.
 * Tails - specifies the number of distribution tails to return.
 * If Tails = 1, TDIST returns the one-tailed distribution.
 * If Tails = 2, TDIST returns the two-tailed distribution.
 * If any argument is non-numeric, TDIST returns the #VALUE! error value.
 * If Deg_freedom < 1, TDIST returns the #NUM! error value.
 * The Deg_freedom and Tails arguments are truncated to integers.
 * If Tails is any value other than 1 or 2, TDIST returns the #NUM! error value.
 * If x < 0, then TDIST returns the #NUM! error value.
 * If Tails = 1, TDIST is calculated as TDIST = P( X>x ), where X is a random variable that follows the t-distribution.
 * If Tails = 2, TDIST is calculated as TDIST = P(|X| > x) = P(X > x or X < -x).
 * Since x < 0 is not allowed, to use TDIST when x < 0, note that TDIST(-x,df,1) = 1 – TDIST(x,df,1) = P(X > -x) and TDIST(-x,df,2) = TDIST(x,df,2) = P(|X| > x).