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Prove that √5 is irrational.
By BYJU'S Exam Prep
Updated on: October 17th, 2023
We have to prove that √5 is an irrational number
It can be proved using the contradiction method
Assuming √5 as a rational number, i.e., can be written in the form a/b where a and b are integers with no common factors other than 1 and b is not equal to zero.
Table of content
√5/1 = a/b
√5b = a
By squaring on both sides
5b2 = a2
b2 = a2/5 …. (1)
It means that 5 divides a2.
It means that it also divides a
a/5 = c
a = 5c
By squaring on both sides
a2 = 25c2
Substituting the value of a2 in equation (1)
5b2 = 25c2
b2 = 5c2
b2/5 = c2
As b2 is divisible by 5, b is also divisible by 5
a and b have a common factor as 5
It contradicts the fact that a and b are coprime
This has arisen due to the incorrect assumption as √5 is a rational number.
Therefore, √5 is irrational.
Summary:
Prove that √5 is irrational.
It is proved that √5 is irrational.
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