Find max(x + y + z)*min(x + y + z)

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In summary, the equation $4^\sqrt{5x+9y+4z}-68\times2^\sqrt{5x+9y+4z}+256=0$ has solutions $2^2$ and $2^6$ for $2^\sqrt{5x+9y+4z}$, giving values of $4$ and $36$ for $5x+9y+4z$. This leads to a minimum value of $4/9$ for $x+y+z$ and a maximum value of $9$, resulting in a product of $4$ for the two values.
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Albert1
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$x,y,z$ are non-negative real numbers ,given:

$4^\sqrt{5x+9y+4z}-68\times2^\sqrt{5x+9y+4z}+256=0$

please find:

$\max(x+y+z)\times \min(x+y+z)$
 
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  • #2
Re: find max(x+y+z)*min(x+y+z)

[sp]Let $\lambda = 2^\sqrt{5x+9y+4z}$. Then the equation becomes $\lambda^2 - 68 \lambda + 256 = 0$, with solutions $\lambda = 4 = 2^2$ and $\lambda = 64 = 2^6.$ Thus $2^\sqrt{5x+9y+4z} = 2^2$ or $2^6$, and so $5x+9y+4z = 4$ or $36$. When $5x+9y+4z = 4$ we get $(x+y+z)_{\min} = 4/9$ by taking $(x,y,z) = (0,4/9,0)$. When $5x+9y+4z = 36$ we get $(x+y+z)_{\max} = 9$ by taking $(x,y,z) = (0,0,9)$. Therefore $(x+y+z)_{\min}\times (x+y+z)_{\max} = 4$.[/sp]
 
  • #3
Re: find max(x+y+z)*min(x+y+z)

Opalg said:
[sp]Let $\lambda = 2^\sqrt{5x+9y+4z}$. Then the equation becomes $\lambda^2 - 68 \lambda + 256 = 0$, with solutions $\lambda = 4 = 2^2$ and $\lambda = 64 = 2^6.$ Thus $2^\sqrt{5x+9y+4z} = 2^2$ or $2^6$, and so $5x+9y+4z = 4$ or $36$. When $5x+9y+4z = 4$ we get $(x+y+z)_{\min} = 4/9$ by taking $(x,y,z) = (0,4/9,0)$. When $5x+9y+4z = 36$ we get $(x+y+z)_{\max} = 9$ by taking $(x,y,z) = (0,0,9)$. Therefore $(x+y+z)_{\min}\times (x+y+z)_{\max} = 4$.[/sp]

from Opalg's mention :
$5x+9y+4z = 4$ or $36$.
for:$4x+4y+4z\leq 5x+4y+9z\leq 9x+9y+9z$
if $5x+4y+9z=4$
then :$4x+4y+4z\leq 4 \leq 9x+9y+9z$
$\therefore x+y+z\geq \dfrac {4}{9}$
if $5x+4y+9z=36$
then :$4x+4y+4z\leq 36 \leq 9x+9y+9z$
$\therefore x+y+z\leq 9$
and we get :$max(x+y+z)\times min(x+y+z)=4$
 

FAQ: Find max(x + y + z)*min(x + y + z)

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The purpose of this equation is to find the maximum possible value of the sum of three variables (x, y, and z) multiplied by the minimum possible value of the same sum. This can be used in various mathematical and scientific applications, such as optimization problems and data analysis.

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