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# If $\alpha +\beta+\gamma= 2\theta$, then $cos \theta+ \cos (\theta- \alpha)+ \cos (\theta- \beta)+ \cos (\theta- \gamma)=$

$\begin {array} {1 1} (1)\;4 \sin \frac{\alpha}{2}. \cos \frac{\beta}{2}. \sin \frac{\gamma}{2} & \quad (2)\;4 \cos \frac{\alpha}{2}. \cos \frac{\beta}{2}. \cos \frac{\gamma}{2} \\ (3)\;4 \sin \frac{\alpha}{2}. \sin \frac{\beta}{2}. \sin \frac{\gamma}{2} & \quad (4)\;4 \sin \alpha.\sin \beta . \sin \gamma \end {array}$

$(2)\;4 \cos \frac{\alpha}{2}. \cos \frac{\beta}{2}. \cos \frac{\gamma}{2}$