dA_prev Assignment 1 week 4

I’m not sure I understand the question. The functions sigmoid_backward and relu_backward are called from linear_activation_backward, right? That function takes an argument dA. That is the dA argument that you pass to sigmoid_backward and relu_backward. If your question is what those functions do, they are provided in an “import” file. You can examine the code by clicking “File → Open” from the notebook and then opening the appropriate utility python file. There is a topic about that on the FAQ Thread, q.v.