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Prove that 3+2root5 is irrational

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Prove that 3+2root5 is irrational
  • 2 answers

Yogita Ingle 4 years, 8 months ago

Letus assume that 3 + 2√5 is a rational number.

Soit can be written in the form a/b
3 + 2√5 = a/b
Here a and b are coprime numbers and b ≠ 0
Solving3 + 2√5 = a/b we get,
=>2√5 = a/b – 3
=>2√5 = (a-3b)/b
=>√5 = (a-3b)/2b
This shows (a-3b)/2b is a rational number. But we know that But √5 is an irrational number.

so it contradictsour assumption.

Our assumption of3 + 2√5 is a rational number is incorrect.
3 + 2√5 is an irrational number

Hence proved

Logeshwari Lokeshwari.D 4 years, 8 months ago

Our Assumation is wrong, it's irrational numbers.
http://mycbseguide.com/examin8/

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