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Title: Square root of two is irrational : truth table LOGICAL PROOF
Description: This is a truth table proof of one of the first calculus (real analysis) topics "irrationality of root two". Here I have provided a truth table chart showing that square root of two is irrational (cannot be expressed in p/q form). The usual approach is by the proof by contradiction method. Here we analyze differently with a truth table chart and finally show, even to skeptics who do not believe quickly, that the statement "square root of two is irrational" is indeed true.

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This is a truth table proof of one
of the first real analysis topics
"irrationality of root two"
...
The usual approach is
i by the proof by contradiction
Here
we
analyze
n method
...


Page 1

Meaning of symbols:


For all



For some



belongs to



Set of all natural numbers



Set of all irrational numbers

Page 2

𝟐 irrationality
𝛼, 𝛽 ∈ ℕ
𝑎≝

𝛼
HCF(𝛼, 𝛽)

𝛽
𝑏≝
HCF(𝛼, 𝛽)



HCF

given
(𝑎 ∈ ℕ)
definitions
(𝑏 ∈ ℕ)

𝛼
𝛽
,
=1
HCF(𝛼, 𝛽) HCF(𝛼, 𝛽)

T
{Theorem}

Page 3



T

HCF 𝑎, 𝑏 = 1 (𝑎, 𝑏 ∈ ℕ)

{definition of 𝑎 and 𝑏}



F

CF 𝑎, 𝑏 = 2

{definition of HCF}



F

𝑎 has factor 2 ^ 𝑏 has factor 2

{definition of CF}











𝑎 has factor 2

𝑎 = 2𝑐 (∃ 𝑐 ∈ ℕ)

2
𝑎 = 4𝑐 2

𝑎2 has factor 2
𝑏 has factor 2

2
𝑏 has factor 2

2
𝑏 = 2© (∀ © ∈ ℕ)
𝑏2 = 2𝑐 2

2𝑏2 = 4𝑐 2

2𝑏2 = 𝑎2

𝑎
2=
𝑏

𝛼
2=
𝛽

2≠

𝛼
𝛽

T

F

F
{by ⑷ and ⑸(i)}

F
{special case of
⑹(iii)}

F

F

{by ⑸(iii) and ⑺(ii)}

{by ⑸(iv)}

T
{definition of ≠}

Page 4

∀ 𝛼, 𝛽 ∈ ℕ, 2 ≠


def

𝛼
𝛽

T
{by exact above 9 steps, ⑼ holds ∀ 𝛼, 𝛽 ∈ ℕ}

2∈ℙ



Page 5


Title: Square root of two is irrational : truth table LOGICAL PROOF
Description: This is a truth table proof of one of the first calculus (real analysis) topics "irrationality of root two". Here I have provided a truth table chart showing that square root of two is irrational (cannot be expressed in p/q form). The usual approach is by the proof by contradiction method. Here we analyze differently with a truth table chart and finally show, even to skeptics who do not believe quickly, that the statement "square root of two is irrational" is indeed true.