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Prove that √p+√q is irrational ,if …

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Prove that √p+√q is irrational ,if p and q are prime numbers . Explain it with easy method
  • 3 answers

? Pranali.A.P ? 5 years, 4 months ago

Search Results Featured snippet from the web Now x, x², p, q and 2 are all rational, and rational numbers are closed under subtraction and division. So (x² - p - q) / 2 is rational. But since p and q are both primes, then pq is not a perfect square and therefore √(pq) is not rational. But this is a contradiction.

Yogita Ingle 5 years, 4 months ago

lets assume that √p is rational,

⇒ √p = a/b ( where 'a' and 'b' are co primes, meaning they don't have any common factors except for 1)

From squaring both sides,

p = a²/b²

⇒pb² = a²

⇒ b² = a²/p

Since 'p' divides a², it also divides 'a' meaning 'a' has a factor of p

Let 'a' = pm (where m is a positive integer) ⇒ a² = p²m²

Now, pb² = a²

pb² = p²m²

pb²/p²= m²

b²/p =m²

∴ 'p' divides 'b' ⇒ 'b' also has a factor 'p'

∴ 'a' and 'b' are not co primes and our assumption was wrong

⇒ √p is irrational

Similarly √q is irrational

∴⇒ √p + √q is irrational

Sumesh ☺️☺️☺️ 5 years, 4 months ago

Let us suppose that √p + √q is rational.  Let √p + √q = a, where a is rational.  = √q = a – √p  Squaring on both sides, we get  q = a2 + p - 2a√p => √p = (a2 + p - q)/2a, which is a contradiction as the right hand side is rational number, while√p is irrational.  Hence, √p + √q is irrational.
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