Question: Elementary simplification

I have the following equation

phi = -arctan(sin(2*theta)*(cos(beta)-1)/(cos(beta)*cos(2*theta)-cos(2*theta)-cos(beta)-1))+theta;

phi = -arctan(sin(2*theta)*(cos(beta)-1)/(cos(beta)*cos(2*theta)-cos(2*theta)-cos(beta)-1))+theta

 

In the denominator I wish to collect the two cos(2*theta) terms  into a single term, as in

(1-cos(beta))*cos(2*theta)

 

Is there a straighforward way of doing it?

 

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