one more

[JeanneMo]

Suppose F varies jointly as x and y and inversely as z squared. If F is equal to 18 when x = 4, y = 3 and z = 2, find the value of F if the values for x, y, and z respectively are doubled.


I had that it would still be 18... is that right?

 

[tkhunny]

Yup. Can you prove it?

 

[JeanneMo]

prove it?

Ha- I followed some formula in the book, but was thrown off by it being the same # so I thought I might be wrong... so prove it? NO, not right this minute, but with the stuff in the book maybe! ;-) THANKS!

 

[tkhunny]

Chicken! :wink:

F = (x*y)/z^2

Double everything.

((2*x)*(2*y))/(2*z)^2 = 4*(x*y)/[4*z^2] = (4/4)*(x*y)/z^2 = F