Which is the quadratic variation equation for the relationship?

y varies directly with x2 and y = 72 when x = 3.

Question

Which is the quadratic variation equation for the relationship?

y varies directly with x2 and y = 72 when x = 3.

whpalmer4 · Answer

if $y$ varies jointly with $x^2$, then $y = kx^2$.  Substitute $y = 72, x=3$ into that equation and solve for $k$.

anonymous · Answer

@whpalmer4   so jointly and directly same thing?

whpalmer4 · Answer

@timo86m jointly means you have something like $z = k x y$ where $z$ varies jointly with $x$ and $y$

jjuden · Answer

y = 8x^2

       y = 24x^2

       y=1/8x^2
    
        y=1/24x^2

anonymous · Answer

aaa but she said directly

whpalmer4 · Answer

Yes, the answer is one of those :-)

anonymous · Answer

direct will be

y=c*x^2


you are given y and x  so solve for c :)  like before

72=c*3^2

whpalmer4 · Answer

$$y = k x^2$$$$y = 72, \, x = 3$$$$72 = k(3)^2$$Solve for $k$

jjuden · Answer

k=8 right?

anonymous · Answer

sorry os broke

anonymous · Answer

you are right

whpalmer4 · Answer

@timo86m Sorry, yes, she did say directly, and I wrote jointly.  The previous problem was a jointly, so I had jointly on my mind :-)  Directly with $x^2$ could be viewed as equivalent to jointly with $x$ and $x$, however!  Aside from the incorrect word, everything else was correct.