Tricky math problem

**ƒ(x)** · May22-09, 03:53 PM

A friend of mine showed this to me a few days ago:

x+y+z=0
x³+y³+z³=3
x⁵+y⁵+z⁵=15

x²+y²+z²=?

An answer must be supported with justification (so that I know that you didn't guess and get lucky).

**-Aladdin-** · May23-09, 12:17 AM

I'm going to ask my math teacher :)

**regor60** · May26-09, 10:47 AM

Originally Posted by ƒ(x)

A friend of mine showed this to me a few days ago:

x+y+z=0
x³+y³+z³=3
x⁵+y⁵+z⁵=15

x²+y²+z²=?

An answer must be supported with justification (so that I know that you didn't guess and get lucky).

Unless you can demonstrate that there is a clever shortcut to this problem which would raise it to the level of a brainteaser, this is just a set of simultaneous equations which is easily solvable with, for example, the Wolfram Alpha website.

**ƒ(x)** · May28-09, 04:30 PM

Originally Posted by regor60

Unless you can demonstrate that there is a clever shortcut to this problem which would raise it to the level of a brainteaser, this is just a set of simultaneous equations which is easily solvable with, for example, the Wolfram Alpha website.

I had no idea that such a site even existed.

**-Aladdin-** · May29-09, 04:20 AM

How do they solve it ?

**LAF** · Jun9-09, 02:18 PM

I got the answer but i cant´t get the values os x, y and z, but i got that x.y.z =

Spoiler

x.y.z=1

**LAF** · Jun10-09, 12:20 PM

Ok...that was prety hard to solve...it took many hours. I hope you have an easier way to get the answer (tricky):

Spoiler

x= 2 cos (20)
y= 2 cos (140)
z= 2 cos (260)
the answer to the question is 6

**LAF** · Jun10-09, 12:24 PM

At a glance:

Spoiler

x = -y-z
x<2 and positive
y not equal z
y and z are negative
x.y.z = 1

**LAF** · Jun10-09, 04:08 PM

OK, I got it...it´s really simple to get the answer to x2+y2+z2=?....

Spoiler

the answer is 6. and you just have to set values to x (positive) y(negative) and z(negative) and calcutale the proportion like: set x=3 y=-2 z=-1, then
^2 = 14 --> ?
^3 = 18 --> 3
^5 = 210 --> 15

so 14 . 18 . 15 = ? . 3 . 210
? = 6

That´s the tricky way...