Peter R. answered 03/06/23
Adjunct Lecturer - Math Department - Borough of Manhattan C.C.
4√(81x12y4) can be broken down into its principal roots as follows:
4√81 = 3
4√x12 = x12/4 = x3, because x3•x3•x3•x3 = x3+3+3+3 = x12
4√y4 = y4/4 = y
Now you can put the all of the factors together.