Question 1074024
The variable x varies jointly with y and z use the given vales to write an equation relating x,y and z.  x=2 when y=3 and z=-4, then find y when x=8 and z =1
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For all such problems, start with this:
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Varying           "directly" or product of "jointlys" or 1 if none 
quantity  = k * ----------------------------------------------------------
                inversely variable or product of "inverselys" or 1 if none
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In this problem the varying quantity is x.
there are no "directly"s or "inverselys", so we have
the product of the jointlys on top and 1 on the bottom:

{{{x=k*(yz/1)}}}

{{{x=k*yz}}}

>>...x = 2 when y = 3 and z = -4...<<

Substitute these values and solve for k:

{{{x=k*yz}}}

{{{(2)=k*(3)(-4)}}}

{{{2=k*(-12)}}}

{{{2/-12=k}}}

{{{-1/6=k}}}

Next substitute -1/6 for k in

{{{x=k*yz}}}

{{{x=expr(-1/6)*yz}}}

That is the complete equation of variation,
which can be used to find any one of the three
variables when two of them are given

>>...find y when x=8 and z=1 <<

Now we substitute those values into

{{{x=expr(-1/6)*yz}}}

and solve for y.

I'll let you do that.  If you have trouble, you
can tell me in the thank-you note form below,
and I'll get back to you by email.  No charge, 
as I do this for fun.  :)

Edwin</pre></font></b>