Trouble solving for the variance

[late monolith]

I know to solve for the mean first by taking the sum of X an dividing by the n variable, but I forgot how to solve the rest of it.
Working on a review sheet for an upcoming test.

[blazing otter]

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[late monolith]

Additionally, when looking up how to solve it online, I was shown a different example that presented the variance equation that displayed the Sum of X squared - the mean value with an exponent of negative two, but I don't remember going over that very last part with the negative exponent

the example I was trying to look at before submitting a post

[fallen ridge]

recall the formulas for variance and standard deviation
and expand the sigma
for example for sigma x rewrite it in the form of x1+x2+...+xn
then use algebraic formulas and etc

[late monolith]

+close