三角比(easy)

cos@ > 0 及 tan@ > 0 => @ 在象限 I
cos@ = 1/2
設 x = 1, r = 2, 則 y = sqrt(2^2 - 1^2) = sqrt(3)
sin@ = y / r = sqrt(3) / 2
tan@ = y / x = sqrt(3) / 1 = sqrt(3)