To translate 3 units to the right, we replace all 'x' terms with (x-3)
g(x) = f(x-3)
f(x) = cos(2x) ..... original function
f(x-3) = cos(2(x-3)) .... replace every x with (x-3)
f(x-3) = cos(2x-6) .... distribute
g(x) = cos(2x-6) is the answer
The g(x) curve is the result of shifting the f(x) curve 3 units to the right.