

_T_r_i_g_o_n_o_m_e_t_r_i_c _F_u_n_c_t_i_o_n_s

     cos(x)
     sin(x)
     tan(x)
     acos(x)
     asin(x)
     atan(x)
     atan2(y, x)

_D_e_s_c_r_i_p_t_i_o_n:

     These functions give the obvious trigonometric func-
     tions.  They respectively compute the cosine, sine,
     tangent, arc-cosine, arc-sine, arc-tangent and arc-
     tangent of two arguments.

_S_e_e _A_l_s_o:

     `Log', `Math'.

_E_x_a_m_p_l_e_s:

     cos(0) == 1
     sin(3*pi/2) == cos(pi)
     x <- rnorm(99)
     all( sin(-x) == - sin(x))
     all( cos(-x) == cos(x))

     x <- 1:99/100
     all(Mod(1 - (cos(x) + 1i*sin(x)) / exp(1i*x)) < 1.1 * .Machine$double.eps)
      2* abs(1 - x / acos(cos(x))) / .Machine$double.eps #-- depends ?
     all(abs(1 - x / asin(sin(x))) <= .Machine$double.eps) # TRUE
     all(abs(1 - x / atan(tan(x))) <= .Machine$double.eps) # TRUE

