def(x)=ln(cos(4x))

Solution for def(x)=ln(cos(4x)) equation:

Simplifying
def(x) = ln(cos(4x))

Multiply def * x
defx = ln(cos(4x))

Remove parenthesis around (4x)
defx = ln(cos * 4x)

Reorder the terms for easier multiplication:
defx = ln(4cos * x)

Multiply cos * x
defx = ln(4cosx)

Remove parenthesis around (4cosx)
defx = ln * 4cosx

Reorder the terms for easier multiplication:
defx = 4ln * cosx

Multiply ln * cosx
defx = 4clnosx

Solving
defx = 4clnosx

Solving for variable 'd'.

Move all terms containing d to the left, all other terms to the right.

Divide each side by 'efx'.
d = 4ce-1f-1lnos

Simplifying
d = 4ce-1f-1lnos