# If $a=\cos\alpha- i \sin \alpha,b=\cos\beta-i \sin\beta,c=\cos\gamma-i\sin\gamma$ then $(a^{2} c^{2} -b^{2})/abc$ is

$(1)\cos 2(\alpha-\beta+\gamma)+i\sin 2(\alpha-\beta+\gamma)$(2)$-2\cos(\alpha-\beta+\gamma)$(3)$-2 i\sin(\alpha-\beta+\gamma)$(4)$2\cos(\alpha-\beta+\gamma)$