In function #f(x) = acosb(x - c) + d#, the amplitude is given by #|a|# and the vertical displacement is given by #d#.
Therefore, your function has a vertical displacement of #5# and an amplitude of #5#. A vertical displacement means you moved the graph up by #d# units from the x axis. The amplitude is the distance between the center line (#y = 5# in this case) and the maximum/minimum points of the function. Thus, the maximum points will be at #(x, 10) and (x, 0)#. The can be summarized as #"minimum in y"<= y <= "maximum in y "#, or in the case of this function, #0 <= y <= 10#.
In conclusion, the domain of #y = 5cos((1/2)(x - pi/4)) + 5 # is #x="all the real numbers" # and the range is #0 <= y<= 10#.
Hopefully this helps!