Which of the ff function cannot be expressed in explicit form of dy/dx

Question

4x+4y=2
xy-y^2=1
ycosx=5

My answer is ycosx=5

Answer 1

clearly #1 can be so expressed.
#2 cannot: y' = y/(2y-x)
#3 can: y = 5secx, so y' = 5secx tanx