Proving 2/5*(2^0.5)-1/7 is Irrational: Elementary Math Proof

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SUMMARY

The discussion focuses on proving that the expression 2/5*(2^0.5)-1/7 is irrational using elementary mathematical principles. The proof employs a contradiction method, asserting that the product of a rational number (2/5) and an irrational number (2^0.5) remains irrational. The proof is validated by assuming the product is rational and demonstrating that this leads to a contradiction, confirming the irrationality of the expression. The consensus is that accepting the irrationality of the square root of 2 is essential for this proof.

PREREQUISITES
  • Understanding of rational and irrational numbers
  • Familiarity with proof by contradiction
  • Basic knowledge of algebraic manipulation
  • Concept of square roots, specifically the irrationality of √2
NEXT STEPS
  • Study the principles of proof by contradiction in mathematics
  • Explore the properties of rational and irrational numbers
  • Learn about the implications of irrational numbers in algebraic expressions
  • Investigate other proofs of irrationality, such as the proof that √2 is irrational
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This discussion is beneficial for mathematics students, educators, and anyone interested in understanding proofs involving irrational numbers and algebraic expressions.

lolo94
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Homework Statement


Proof 2/5*(2^0.5)-1/7 is irrational

Homework Equations

The Attempt at a Solution


I did this by splitting the expression and setting contradictions
2/5->rational
2^0.5->irrational

Proof first rational times irrational is irrational

Proof by contradiction

Assume the product is rational
let rational be x/y irrational s and the product u/t

rational*irrational=x/y*s=u/t
s=uy/tx

Contradiction s can't be rational

and then I do the same thing for irrational-rational

Is that the right approach?
 
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Sure-- a proof is a proof, and that would prove it. The question I have is if you are allowed to take as given that the square root of 2 is irrational, but if you are, proof by contradiction is certainly the way to go.
 

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