Deriving harmonic mean

Course Q&A Machine Learning Specialization Advanced Learning Algorithms
1

Out of curiosity, how does one get from 1 / ( 1/2 (1/P + 1/R) ) to 2 (PR / P+R) ?

2

I think that’s just a bit of algebra.

3

Yes, I believe.

It is pretty easy to get from:
1 / ( 1/2 (1/P + 1/R) )
to
2 / (1/P + 1/R)

But from there to

2PR / (P+R) seems just incomprehensible.

4

Hello @Lassi_Elo, we can just focus on this → 1/P + 1/R and the next step would be to find the common denominator which is PR. Can you continue from here?

1 Like
5

Thanks, I got it! I forgot that I can just focus on one part of the equation at a time.

6

You are welcome @Lassi_Elo!