Andrew Ng Links

https://www.youtube.com/watch?v=E-aX2yK3Uws

1.2.1 Model Representation by Andrew Ng

https://www.youtube.com/watch?v=lM49Mz3mIXE

1.2.2 Cost Function by Andrew Ng

https://www.youtube.com/watch?v=CFeCaFUnhlM

1.2.3 Cost Function Intuition I by Andrew Ng

https://www.youtube.com/watch?v=iRQpg_CZNW4

1.2.4 Cost Function Intuition II by Andrew Ng

https://www.youtube.com/watch?v=yFPLyDwVifc

1.2.5 Gradient Descent

https://www.youtube.com/watch?v=rIVLE3condE

1.2.6 Gradient Descent Intuition

https://www.youtube.com/watch?v=q0pm-ZweMfk

1.2.7 Gradient Descent For Linear Regression

https://www.youtube.com/watch?v=yR2ipCoFvNo

Lecture 2.3 — Linear Regression With One Variable | Cost Function Intuition #1 | Andrew Ng

https://www.youtube.com/watch?v=0kns1gXLYg4

Lecture 2.4 — Linear Regression With One Variable | Cost Function Intuition #2 | Andrew Ng

https://www.youtube.com/watch?v=F6GSRDoB-Cg

Lecture 2.5 — Linear Regression With One Variable | Gradient Descent — [ Andrew Ng]

https://www.youtube.com/playlist?list=PLpFsSf5Dm-pd5d3rjNtIXUHT-v7bdaEIe

Another explanation here is also good and list downs the formulae as per popular internet posts today, but it needs to be verified for authenticity, because there seem to be some differences, for example the definition of SGD with momentum in this link uses exponential averages of gradients where as some people do not use it, such as this one.