3 ms·

Would somebody explain this step in his explanation? http://izbicki.me/blog/wp-content/plugins/optimized-latex/image.php?image=tex_240ba03b0952b1e7d16eb8570d9d

by afc 14y ago

Would somebody explain this step in his explanation? http://izbicki.me/blog/wp-content/plugins/optimized-latex/image.php?image=tex_240ba03b0952b1e7d16eb8570d9d1ee5.png http://izbicki.me/blog/wp-content/plugins/optimized-latex/im... How does he go from (a - b)^2 to a^2 - b^2? What am I missing?

jgeralnik 14y ago
That's the definition of variance. Look here: http://en.wikipedia.org/wiki/Variance#Definition http://en.wikipedia.org/wiki/Variance#Definition
andrewcooke 14y ago
b in the case given is the mean. so it's defined as sum(a)/n. so the "ignored" term is sum(a-sum(a)/n)) which is zero.
deleted 14y ago
[deleted]