The value of $\tan 81^{\large \circ}-\tan 63^{\large\circ}-\tan 27^{\large\circ}+\tan 9^{\large \circ}$ is

Question

$(a)\;1\qquad(b)\;2\qquad(c)\;3\qquad(d)\;4$

Comments

http://math.stackexchange.com/questions/823619/calculate-tan9-circ-tan27-circ-tan63-circ-tan81-circ