1. The problem statement, all variables and given/known data For the following dimensional equation, find the base dimensions of the parameter f: M M-3 = a cos( f L ) 2. Relevant equations M represents mass, a represents acceleration due to gravity, in terms of mass * length over seconds squared [[M * L]/[t2]] where L represents length and t represents time. For example, solving for k in the equation: ML2 = k L t M2 results in k = L M-1 t-1 3. The attempt at a solution The answer, which is given, is L-1, So I got cos-1(M-2 a-1) = f L the output of the cos-1 function results in a dimensionless unit of measure (radian/degree). Therefore, c = f L where c is a constant/dimensionless quantity, therefore f = L -1 The problem is that I cannot understand how the inverse cosine function works in this sense. Can its input be "dimensionally inequivalent", I cant find the word for it.