Hello friends!

Question is:

The harmonic mean of 2 numbers,aandbis

____2____

_1_+_1_

a______b

The harmonic mean of 3 numbers,a,bandc, is

______3______

_1_+_1_+_1_

a______b____c

a)Simplify the expressions for 2 and 3 numbers and find a simplified expression for the harmonic mean of 4 numbers.

b)Find the harmonic mean of the numbers 2, 3, 4 7 and 9.