Is there a way to show the sum of any different square root of prime numbers is irrational? For example, √2+√3+√5+√7+√11+√13+√17+√19 should be a irrational number.
One approach I used is to let the sum be a solution of an even polynomial f(x)with integer coefficients and prove by induction that by adding another √pk+1. The new polynomial can be written as f(x+√pk+1)f(x−√pk+1)
where f(x+−√pk+1)=P(x)+−Q(x)√pk+1,
where P(x) is an even plynomial and Q(x)
is an odd polynomial.
The new polynomial can be written as P2(x)−Q2(x)pk+1.
Assume it has a rational solution a, we must haveP(a)=Q(a)=0.
My calculation stopped here since I can't find any contradiction result from this. Can anyone continue this proof, or has other better way to solve this? Thanks!
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