1. ## Basic Question about Variance

For example for variance of delta x, some sources have it as (delta*x)^2 with a bar on top, and others show it as <(delta*x)^2>. Are they referring to the same thing?

Thanks.

2. dont the authors define their notation the first time they use it?

$\displaystyle \delta_x ^2$ is a notation i've seen for the variance before

$\displaystyle \hat{\delta_x ^2}$ is a plausible notation for the estimate of the variance

$\displaystyle \bar{\delta_x ^2}$ i've never seen and wouldn't understand if i saw it.

NB i edited the content of this post while OP was typing the reply below

3. Here are the sources. The first is a youtube video (watch at the beggining he says variance of delta x), and for the second one, go to page 10, equation 2.19

YouTube - The Basics of Physics I - How to derive the uncertainty principle

http://farside.ph.utexas.edu/teaching/qmech/qmech.pdf