(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

The vector [tex]\vec{E}_n[/tex] is the vector sum of the two vectors [tex]\vec{E}_r[/tex] and [tex]\vec{E}_{\theta}[/tex], which are perpendicular to each other (see attached picture). Calculate the magnitude of [tex]\vec{E}_n[/tex].

3. The attempt at a solution

[tex]E_n=E_r\cos(\theta)+E_{\theta}\sin(\theta)[/tex]

But this is wrong. It's supposed to be a minus sign instead of a plus. I have no idea why. I thought it would be to simply add the components of [tex]\vec{E}_r[/tex] and [tex]\vec{E}_{\theta}[/tex] along the direction of [tex]\vec{E}_n[/tex]. Why the minus sign?

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# Homework Help: Vector sum, polar coordinates

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