Understand maths behind deep learning

Can anyone gives me some suggestions and resources to learn the maths of deep learning, especially the backpropagation. I have been teaching myself deep learning for 3 months and still can’t understand the maths of backpropagation, I would like to know how to understand the maths. Thanks!

Look for YouTube videos by Andrew Ng. Really good presentation and insight.

Here’s an example:

Also Khan Academy to study partial differential equations…