Identify the variation as direct, inverse, joint or combined. f= kw1w2/s
a: direct
b: inverse
c: joint
d: combined

OPTION D.

Step-by-step explanation:

It is important to remember that a variation is Combined when a variable depends on two or more other variables. Then, this will vary directly with some of these variables and inversely with the others.

In this case, you have the following expression:

Assuming that "k" is the constant of variation, you can observe that   varies jointly as and and inversely as .

 Therefore, the variation is: COMBIINED.