DotProduct Method

Hello, All,
Can anyone explain to me the method of DotProduct in the API? I understand the vectors DotProduct mathematically but it seems like I miss something!
Also, when I compared the DotProduct method from API and the Dot method in Dynamo, they gave me different results. So, I am very confused.
Note: My aim is to project a point onto a plane.
Thank you! I appreciate every help.

You can see it here :Dot Product And Cross Product In Dynamo | Hồ Văn Chương


Thanks for your article, Chuong.
I wonder if you have it in English?

it should be same:

From dynamo:

From Revitapi:

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you may refer to here: