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Prove that √5 irrational?
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Prove that √5 irrational?
Proof that √5 is irrational

Assumption: √5 is a rational number.


Let √5 be expressed as a fraction in its simplest form, i.e.

√5 = a/b, where a and b are coprime integers (i.e. they have no common factors).


Step 1: Squaring both sides

Squaring both sides of the equation, we get:

5 = a^2/b^2


Step 2: Rearranging the equation

Multiplying both sides by b^2, we get:

5b^2 = a^2


Step 3: Analyzing the equation

Since a^2 is a multiple of 5, we can conclude that a must also be a multiple of 5.

Therefore, we can express a as 5k, where k is an integer.

Substituting this value of a in the equation, we get:

5b^2 = (5k)^2

5b^2 = 25k^2

b^2 = 5k^2


Step 4: Analyzing the equation

Now, we can see that b^2 is a multiple of 5, which means that b must also be a multiple of 5.

However, this contradicts our initial assumption that a and b are coprime.

Therefore, our assumption that √5 is a rational number must be false.


Conclusion:

Thus, we have proved that √5 is an irrational number.
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Prove that √5 irrational?
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