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For this case we have that by definition, a direct variation is given by:

Where:
k: It is the constant of proportionality of the variables.
On the other hand, we have that the inverse variation is given by:

Where:
k: It is the constant of proportionality of the variables.
In this way, the correct option is: 
ANswer:
Option A
if we name that part x, then we can say
1/x = 1/a + 1/b
Answer:
Step-by-step explanation:
total degrees of a line is 180
4x+20+60=180
4x=100
X=25
Well I don't know. Let's figure it out together.
You said (a number) divided by 12 gives you 9 .
A fraction is the easiest way to show division, so
you can write this equation:
(number) / 12 = 9
Now you can multiply each side of the equation by 12 .
When you do that, you have ...
number = 9 x 12
<em>number = 108</em> .
Now you know how to find it. That's even better than just
having the answer.