I am trying to understand the following simplification.
I cannot see how to get from the one step to the other.
and then (how do they get to this step?)
and then (very obviously)
It can be seen on wolfram mathworld:
Correlation Coefficient -- from Wolfram MathWorld
I get the following.
How does the simplification from step 2 to step 3 happen.
My simplification is not the same, and I don't see how to make it simpler.