answersLogoWhite

0


Best Answer

The proof that the square root of 5 is irrational is exactly the same as the well-known proof that the square root of 2 is irrational - except using 5 in place of 2. We can prove a more general result: the square root of any prime is irrational.

First of all, we require the lemma:

for any prime p, and integer x,

p|x2 ⇒ p|x

That is, if x2 is divisible by p, then so is x.

Proof:

The prime factorization of x2 necessarily contains p at least once, since it is divisible by p. But it also has to contain an even power of every prime, since it is the prime factorization of a square. Therefore, it contains p at least twice, and its square root, x, contains p at least once: that is, x is divisible by p.

Now, given a prime p, assume that its square root is rational. Then, it may be written in the form a/b, where a and b have no common factors (that is, the fraction a/b is in lowest terms). This is always possible for any nonzero rational number. Since this quantity is the square root of p, its square equals p, that is

(a/b)2 = p

a2/b2 = p

a2 = pb2

Now, pb2 is a multiple of p, so a2 must be too. And, using the result above, this means that a must be a multiple of p also. Thus, there exists an integer c such that

a = PC

Then,

(PC)2 = pb2

p2c2 = pb2.

Since p is not zero, we may divide both sides by p to obtain

PC2 = b2

That is, b2 is divisible by p also, and thus b is divisible by p.

Since a and b were both divisible by p, the fraction a/b could not have been in lowest terms, which contradicts our initial assumption. Therefore, the square root of p cannot possibly be a rational number. Since 5 is prime, the proof is complete.

User Avatar

Wiki User

12y ago
This answer is:
User Avatar

Add your answer:

Earn +20 pts
Q: Where can i find Proof square root of 5 is irrational?
Write your answer...
Submit
Still have questions?
magnify glass
imp
Related questions

Why is the square root of 33 irrational?

Most high school algebra books show a proof (by contradiction) that the square root of 2 is irrational. The same proof can easily be adapted to the square root of any positive integer, that is not a perfect square. You can find the proof (for the square root of 2) on the Wikipedia article on "irrational number", near the beginning of the page (under "History").


Is the square root of 32 an irrational or a rational number?

The square root of a positive integer can ONLY be:* Either an integer, * Or an irrational number. (The proof of this is basically the same as the proof, in high school algebra books, that the square root of 2 is irrational.) Since in this case 32 is not the square of an integer, it therefore follows that its square root is an irrational number.


How do you find an irrational square root?

An irrational number is a number that never ends. An example of an irrational square root would be the square root of 11.


Is the square root of a 143 a irrational number?

Yes. The square root of a positive integer can ONLY be either:* An integer (in this case, it isn't), OR * An irrational number. The proof is basically the same as the proof used in high school algebra, to prove that the square root of 2 is irrational.


Is the square root of 3 rational?

Root of '3' is NOT rational. It is an IRRATIONAL Number. To 9 d.p. it is sqrt(3) = 1.732050808.... NB THE square roots of prime numbers are irrational , just like 'pi = 3.141592....'. NNB A irrational number, put casually, is a number were the decimals go to inifinty and there is no regular order in the number2.


Why is the square root of 10 irrational?

The argument why the square root of 2 is irrational can be found in most high school algebra books. You can also find this proof, and several other proofs, that the square root of 2 is irrational, in the Wikipedia article "Square root of 2".The same argument can be applied to the square root of any natural number that is not a perfect square.


Is they sqare root of 94 irrational or irrational?

The square root of 94 is an irrational number


Why is 3 square root of 2 is irrational?

sqrt(2) is irrational. 3 is rational. The product of an irrational and a non-zero rational is irrational. A more fundamental proof would follow the lines of the proof that sqrt(2) is irrational.


Is the square root of 200 rational or irrational?

The square root of 200 is irrational.


Is the square root of 28 irrational or rational?

irrational


Is the square root of -255 rational or irrational?

Irrational (and a multiple of i), as the square root of 255 is irrational.


Is the square root of 11 rational or irrational?

The square root of 11 is an irrational number