Cannot compile equation in LaTeX- Help with code please

[su2111]

Hello!
I have been trying to get this equation to work in my LaTeX document, I do not really see any issues with it so if somebody could give some guidance that would be really helpful.

Code:

\begin{equation}
{\bf{R}} = \sum_{i=1}^{N}_{{\bf{u}}_{i}}
\end{equation}

Thank you

 

[su2111]

Sorry! No need for help, I figured out what was wrong!

 

[Arkuski]

I had trouble figuring out the dollar signs as well.