View Full Version : Terrible roots
lemon14
Oct 5, 2010, 06:53 AM
\sqrt[1+2x-y^2]{\sqrt[1+2y-z^2]{\sqrt[1+2z-x^2]{x+y+z}}}, x,y,z\epsilon N \Longrightarrow x,y,z = ?
I have no idea how to get started. I fancy that I don't have to calculate all the arguments :-/
Unknown008
Oct 5, 2010, 07:31 AM
\sqrt[1+2x-y^2]{\sqrt[1+2y-z^2]{\sqrt[1+2z-x^2]{x+y+z}}} = (x+y+z)^{(\frac{1}{1+2z-x^2})(\frac{1}{1+2y-z^2})(\frac{1}{1+2x-y^2})}
Given x,\ y,\ z\ \in\ N\ \Longrightarrow\ x,\ y,\ z = ?
Is that it?
lemon14
Oct 5, 2010, 07:35 AM
I'm sorry, I don't know how much it should equal, I only know that I have to find out the values for x,y,z. How did you get this?
Unknown008
Oct 5, 2010, 07:43 AM
In the same way that we know that:
\sqrt{x} = x^{\frac12}
If we had \sqrt{\sqrt{\sqrt{x}}} = \sqrt{\sqrt{x^{\frac12}}} = \sqrt{x^{(\frac12)^2}} = x^{(\frac12)^3}
lemon14
Oct 5, 2010, 08:00 AM
Ok, then it means that 1+2x-y^2=1+2y-z^1=1+2z-x^2?
Unknown008
Oct 5, 2010, 08:06 AM
Oh shoo sorry sorry sorry :(
I didn't notice that the roots were different in each case :(
I'm editing my post.
Okay, I corrected my previous mistake and it seems that you need to expand.
But the thing is, I never encountered such a problem and I don't know how to solve it :(
I just wanted to clarify what you were asking.
I don't know if it's right, but that's what I think:
To find the roots, we need to equate the expression to zero.
So, we have:
(x+y+z)^{(\frac{1}{1+2z-x^2})(\frac{1}{1+2y-z^2})(\frac{1}{1+2x-y^2})} = 0
But whatever be the power of (x+y+z), it'll be greater than zero if x+y+z \neq 0
So, we need to find when x + y + z = 0
But for that... there are infinite solutions :(
EDIT: "it'll be greater than zero if x+y+z \neq 0" considering |x+y+z|
lemon14
Oct 5, 2010, 09:01 AM
Ok, I'll let you know if I figure out how to solve it.
lemon14
Oct 6, 2010, 09:34 AM
I was thinking what if we would write: \{1+2x-y^2>1\\1+2y-z^2>1\\1+2z-x^2>1, then sum them up: 3+2(x+y+z)-(x^2+y^2+z^2)>3
(x^2+y^2+z^2)-2(x+y+z)<0 ? But from now on I don't know how to find the values :(
lemon14
Oct 9, 2010, 04:43 AM
the solution:
\{1+2x-y^2\geq 2\\ 1+2y-z^2\geq 2\\ 1+2z-x^2\geq 2
y^2-2x+1\leq 0\\ z^2-2y+1\leq 0\\ x^2-2z+1\leq 0
(x^2-2x+1)+(y^2-2y+1)+(z^2-2z+1)\leq 0
(x-1)^2+(y-1)^2+(z-1)^2\leq 0
(x-1)^2+(y-1)^2+(z-1)^2 cannot be <0 so:
(x-1)^2+(y-1)^2+(z-1)^2=0
\Rightarrow\{x=1\\y=1\\z=1
Unknown008
Oct 9, 2010, 06:02 AM
Wow, I never saw that way of solving...
And I don't even understand how you got greater than or equal to 2... I guess I'll learn it some other time :)
lemon14
Oct 10, 2010, 03:50 AM
It is not that difficult: the littlest degree of a root is 2 and here the degrees can be either 2 or greater, they cannot be 1 or smaller. Then I put them into a system of inequalities and made some calculations. The problem wouldn't have been so difficult if I thought of this little rule. I'm sorry if I am not very clear, but I don't have the specific vocabulary to explain it as I'd like to.