Questions   
Sort: 
 #5
avatar
0
May 20, 2019
 #2
avatar
0
May 20, 2019
May 19, 2019
 #5
avatar+129840 
0
May 19, 2019
 #7
avatar+6251 
+1

I am seeing a pattern that the critical points obey.

 

In this problem https://web2.0calc.com/questions/urgent-pls-help_1 we have

 

\(\left(x + 2y+4z\right)\left(\dfrac 4 x + \dfrac 2 y + \dfrac 1 z\right)= \\~\\ 4\left(x + 2y+4z\right)\left(\dfrac{1}{x}+\dfrac{1}{2y}+\dfrac{1}{4z}\right)\)

 

The critical point in this case occurs at 

 

\((x,y,z) = \left(1,\dfrac 1 2,\dfrac 1 4\right)\)

 

I.e. the first critical point coordinate is 1 and the ratio of the critical point coordinates is inverse of that of the ratio of the coordinates in the expression.

 

In the problem at hand we expect the y coordinate of the critical point will be such that

 

\(x^3 = 1 \Rightarrow x = 1\\~\\ 5y^3 = 1 \Rightarrow y = \dfrac{1}{5^{1/3}}\\~\\ 25z^3 = 1 \Rightarrow z = \dfrac{1}{5^{2/3}}\)

 

This would have been modified somehow if the denominator were not symmetric in x,y,z, but in this case it is.

May 19, 2019

3 Online Users

avatar
avatar