Question 164611
Find an equation of variation where y varies jointly as x and z and 
inversely as the square of w and y=20 when x=-0.5, z=4, and w=5.
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y = k[(xz)/w^2] 
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Find "k":
20 = k(-0.5)(4)/5^2

-2k = 20*25
k = -250
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EQUATION:
y = -250xz/w^2
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Cheers,
Stan H.