# Where is this term coming from?

• I
bigmike94
TL;DR Summary
I am back again to ask for your mathematical help.
I got the same result apart from that extra x in the second term? I have boiled it down to that it must have come from maybe the x hat j hat and z hat part of the product rule? Any help would be grateful thank you!

## Answers and Replies

Gold Member
It comes from numerator of the formula above, x i-hat.

bigmike94
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@bigmike94 can you write down what ##A_x## is?

bigmike94
It comes from numerator of the formula above, x i-hat.
Yeah I had a guess what assumed that was it but why is it included and not y or z aswell? Maybe I am missing an i hat which will get rid of the j and z hat cos of the dot product?

bigmike94
@bigmike94 can you write down what ##A_x## is?
I’m not sure how to type maths in here but I think you have just helped me crack it, because it’s in the x direction only we ignore y hat and z hat, then In the product rule you’re left with the extra x.

I’m not sure if that makes sense to you? But yeah I think I get it now thank you

Science Advisor
Homework Helper
Gold Member
2022 Award
I’m not sure how to type maths in here but I think you have just helped me crack it, because it’s in the x direction only we ignore y hat and z hat, then In the product rule you’re left with the extra x.

I’m not sure if that makes sense to you? But yeah I think I get it now thank you
By definition $$\vec A = A_x \hat i + A_y \hat j + A_z \hat k$$This can also be expressed as:$$A_x = \vec A \cdot \hat i$$

You need to learn some LaTex:

https://www.physicsforums.com/help/latexhelp/

bigmike94