Can You Get This With One Chance?

How many unique integer tuples are solutions for the equation x 2 + y 2 + z 2 = 3 x^2 + y^2 + z^2 = 3 ?

2 8 1 \infty

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4 solutions

Since x 2 x 2 + y 2 + z 2 = 3 x^2 \leq x^2 + y^2 + z^2 = 3 , hence x 3 |x| \leq \sqrt{3} . Since x x is an integer, we have x = 1 , 0 , 1 x= -1, 0, 1 . However, if x = 0 x=0 , then we can't get y 2 + z 2 = 3 y^2 + z^2 = 3 . Hence, x x must be either 1 or -1. We have the same conclusion for y , z y, z , thus x , y , z x,y,z can be either 1 1 or 1 -1 .

Now there are 2 × 2 × 2 = 8 2 \times 2 \times 2 = 8 solutions.

( 1 , 1 , 1 ) (1,1,1)

( 1 , 1 , 1 ) (1,1,-1)

( 1 , 1 , 1 ) (1,-1,1)

( 1 , 1 , 1 ) (1,-1,-1)

( 1 , 1 , 1 ) (-1,1,1)

( 1 , 1 , 1 ) (-1,1,-1)

( 1 , 1 , 1 ) (-1,-1,1)

( 1 , 1 , 1 ) (-1,-1,-1)

yup.. aboves is the correct answer....i thought the same that x,y,z will be sure both 1 and -1 but i totally forgot the combination :-( .. thus i ticked 2 ... >:-( ahh feeling angry on myself !!!!!

Anuj Sharma - 7 years, 2 months ago

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Did you know, I got a very bad dream about this XD, When I was sleeping, I dreamed about getting this question wrong again. My rating dropped down to 17XX (21XX in real life). I was angry, so I did 100 problems about number theory for hours! In my dream! Too bad I just did till 94 and my mom woke me up. :<

Samuraiwarm Tsunayoshi - 7 years, 2 months ago

I made the same mistake... I'm really annoyed...

Alex Pacheco - 7 years, 2 months ago

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i know how it feels.......... :-(

Anuj Sharma - 7 years, 2 months ago

I feel very excited to do this problem. It's a problem that challenge me.

Pikkanate Angaphiwatchawal - 7 years, 2 months ago

the given equation is a sphere . it has infinetly many points

Kamalnath Kali - 7 years, 2 months ago

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The approach is good Kamal but I guess you forgot about the integral solutions.

Rohit Madaan - 7 years, 2 months ago

I want to know that why can't 2 and 3 ( and therefore -2 &-3) considered to be in the set..... e.g. let x be 1 and y be 2 then z will be 0. Then also the equation would be valid.....consider x to be 3 then y and z would be 0 which also can be a solution.....in that case..there can be many more solutions.. Please correct me if I am wrong.

Swaroop Sahoo - 7 years, 2 months ago

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It is X^2 and not only X.

Niranjan Khanderia - 7 years, 2 months ago

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DamnIT!..I used that but completely missed it..Me at fault

Swaroop Sahoo - 7 years, 2 months ago

The answer of infinity should be removed as that is a correct answer in the complex plane

Levi Clouser - 5 years, 11 months ago

I used this method too!

Hua Zhi Vee - 4 years, 11 months ago
Ahaan Rungta
Apr 4, 2014

Note that x , y , z { 1 , 1 } x, y, z \in \{ -1, 1 \} , so there are 2 3 = 8 2^3 = \boxed {8} solutions.

Shawn Chao
Apr 2, 2014

2 > x , y , z > 2 -2 > x,y,z > 2 because 2 2 > 3 2^{2} > 3 and ( 2 ) 2 > 3 (-2)^{2} > 3

x , y , z = 1 , 1 , 0 x, y, z = 1, -1, 0

Assuming without loss of generalities that x = 0 , 0 + y 2 + z 2 = 3 x = 0, 0 + y^{2} + z^{2} = 3 has no integer solutions.

Assuming WLOG that x = 0 x = 0 and y = 0 , 0 + 0 + z 2 = 3 y = 0, 0 + 0 + z^{2} = 3 means that z = 3 z = \sqrt{3} , which is irrational.

x x \neq 0 0

Thus, x , y , z , = 1 , 1 x, y, z, = 1, -1

Therefore, there are two combinations for each variable 2 × 2 × 2 = 8 2 \times 2 \times 2 = 8

i thought x, y and z must be different numbers

Cedric Tan - 7 years, 2 months ago

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I think a tuple in this instance is merely a list (of 3: x,y,z), so we needed to find unique combinations. Sadly I did not know this until I clicked 'discuss solution'! :-(

Martin Gray - 4 years, 12 months ago
John Samuel
Jun 29, 2015

there are theree spots x, y and z to fit -1 and 1, which means we have 2 x 2 x 2 = 8 opitons in which -1 and 1 can be arranged into x, y, z to satisfy the given equation

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