2 tan - trigonometric tangent
9 eps nonzero real, defaults to epsilon()
14 Calculate the tangent of x to a multiple of eps, with error less
15 in absolute value than .75 * eps.
18 > print tan(1, 1e-5), tan(1, 1e-10), tan(1, 1e-15), tan(1, 1e-20)
19 1.55741 1.5574077247 1.557407724654902 1.55740772465490223051
22 unlike sin and cos, x must be real
26 NUMBER *qtan(NUMBER *x, NUMBER *eps)
29 sin, cos, sec, csc, cot, epsilon