# How to derive dZ\_\[1\]

**URL:** <https://community.deeplearning.ai/t/how-to-derive-dz-1/345836>\
**Category:** Neural Networks and Deep Learning\
**Tags:** coursera-platform\
**Created:** [May 29, 2023, 3:54am UTC](https://community.deeplearning.ai/t/how-to-derive-dz-1/345836 "2023-05-29T03:54:55Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![Well\_Zhang](https://avatars.discourse-cdn.com/v4/letter/w/f4b2a3/32.png) [@Well\_Zhang](https://community.deeplearning.ai/u/Well_Zhang)\
**Post date:** [May 29, 2023, 3:54am UTC](https://community.deeplearning.ai/t/how-to-derive-dz-1/345836/1 "2023-05-29T03:54:55Z")

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Hi,

In the back propagation video how does Andrew get the dZ\_[1] result as W\_[2].T dZ\_[2] \* g\_[1]'(Z\_[1])?

He skips the derivative of da\_[1] so I have no idea how to get dZ\_[1].

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**Author:** ![paulinpaloalto](https://sea1.discourse-cdn.com/dlai/user_avatar/community.deeplearning.ai/paulinpaloalto/32/187_2.png) [@paulinpaloalto](https://community.deeplearning.ai/u/paulinpaloalto)\
**Post date:** [May 29, 2023, 4:33am UTC](https://community.deeplearning.ai/t/how-to-derive-dz-1/345836/2 "2023-05-29T04:33:06Z")

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The point is that he doesn’t explain any of this really. This course is designed not to require knowledge of calculus. That’s the good news. But of course that means the bad news is that you just have to accept the formulas as he gives them to you.

[Here’s a thread](https://community.deeplearning.ai/t/w3-a1-ex-6-whats-the-link-between-dz-1-and-w-2-equation/221355/2) that discusses this in more detail and points you to some other resources.

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<div class="post-metadata">

**Author:** ![Well\_Zhang](https://avatars.discourse-cdn.com/v4/letter/w/f4b2a3/32.png) [@Well\_Zhang](https://community.deeplearning.ai/u/Well_Zhang)\
**Post date:** [May 29, 2023, 4:34am UTC](https://community.deeplearning.ai/t/how-to-derive-dz-1/345836/3 "2023-05-29T04:34:41Z")

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Okay i see. Appreciate it

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<div class="post-metadata">

**Author:** ![paulinpaloalto](https://sea1.discourse-cdn.com/dlai/user_avatar/community.deeplearning.ai/paulinpaloalto/32/187_2.png) [@paulinpaloalto](https://community.deeplearning.ai/u/paulinpaloalto)\
**Post date:** [May 29, 2023, 4:35am UTC](https://community.deeplearning.ai/t/how-to-derive-dz-1/345836/4 "2023-05-29T04:35:45Z")

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And [here’s another thread](https://community.deeplearning.ai/t/the-intuition-of-db-l-dz-l-and-da-l-1-w-l-1-dz-l/338761) on this same subject.