How Do We Prove That All Variables Are Zero If Their Squares Sum to Zero?

  • Thread starter evagelos
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In summary, the conversation discusses how to prove that if the sum of n squares is equal to 0, then each individual square must also be equal to 0. The idea of using induction is suggested, but it is debated whether it is necessary. Another approach using the fact that if a + b = 0, then either a = b = 0 or a = -b (not equal to 0) is proposed.
  • #1
evagelos
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Every body knows that:

[tex]x_{1}^2+x_{2}^2...x_{n}^2 =0\Longrightarrow x_{1}=0\wedge x_{2}=0...\wedge x_{n}=0[/tex].


But how do we prove that?

Perhaps by using induction?

For n=1 .o.k

Assume true for n=k

And here now is the difficult part .How do we prove the implication for n=k+1??
 
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  • #2
Induction sounds like a bit of overkill here, but if you insist...
Of course it is true that if
[tex]a + b = 0[/tex]
then either a = b = 0, or a = -b (not equal to 0).
You can use this for
[tex]a = x_1^2 + x_2^2 + \cdots + x_n^2, \quad b = x_{n + 1}^2[/tex]
and use that [itex]x_i^2 \ge 0[/itex] for all i.
 

FAQ: How Do We Prove That All Variables Are Zero If Their Squares Sum to Zero?

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