One of the questions in the C4 W4 Quiz asks about the number of output units of the landmarks.

"Question:

When building a neural network that inputs a picture of a person’s face and outputs N landmarks on the face (assume that the input image contains exactly one face), we need two coordinates for each landmark, thus we need 2N output units. True/False?"

The answer is marked as True. However, doesn’t the output need one more unit telling the probability of whether there is a face or not? At least that’s how I understood Andrew’s explanation (at 2:37 of the recording). Thus, 2N+1. His note says 129 units output for 64 landmarks. Can someone explain why the Quiz says 2N is correct?

The thing is after I tried (1,2N), it said wrong, giving the reason " y hat is column vector, not row vector". Then I tried the last option, but still wrong. That’s why I am confused.

Thank you for the confirmation. At lease I have an answer.