to graph that just make a table of values for x and y, in the table plug in x values and find out their corresponding y values and graph them for example, x=-6
-6 cos (5/2(-6)-75 degrees) = 0, now graph the points (-6,0) now plug in x=6, y would be -3 so plot (6,-3) as well
do that until you have enough points to make a rough sketch of the graph.