Help please please please please

I'm being volume of cylinder with 13 in. radius and 30 in height answer choices in pic

Find the value of the cosine for angle a

The construction of copying qpr is started below. the next step is to set the width of the compass to the length of ab. how does this step ensure that a new angle will be congruent to the original angle? by using compass take the measures of angle and draw the same arc according to it.