# Questions on how the projection works

**URL:** <https://community.deeplearning.ai/t/questions-on-how-the-projection-works/638203>\
**Category:** Linear Algebra for Machine Learning and Data Sc...\
**Tags:** week-module-4\
**Created:** [May 31, 2024, 6:25am UTC](https://community.deeplearning.ai/t/questions-on-how-the-projection-works/638203 "2024-05-31T06:25:52Z")\
**Posts on this page:** 1\
**Showing post:** 5

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**Author:** ![rmwkwok](https://sea1.discourse-cdn.com/dlai/user_avatar/community.deeplearning.ai/rmwkwok/32/126977_2.png) [@rmwkwok](https://community.deeplearning.ai/u/rmwkwok)\
**Post date:** [August 28, 2025, 7:50am UTC](https://community.deeplearning.ai/t/questions-on-how-the-projection-works/638203/5 "2025-08-28T07:50:31Z")

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Hello @Bio_J,

Let me put it this way - when you take the dot product of a vector with a unit vector, you get the projection length of the vector along that unit vector. You want to prove this? Try, and I can provide a starting point:

> **Click here for the starting point**
>
> ![image](https://global.discourse-cdn.com/dlai/original/3X/c/4/c48a5b07ca2850f7a5e35bd9ab5fc9ba1f2f8225.png)

Given the statement above, if you need the projection length of any vector on y = x, then ask youself: what’s the unit vector along y = x? If you get the right answer, you will find some square root of 2.

You want to know the projection of the vector (1.2, 1.6) on y = x? You take the dot product of this vector with the unit vector.

Cheers,  
Raymond

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