2 thoughts on “27. Prove that 2- root 5 is irrational, given that root <br />5 is irrational. ”
If possible, let us assume 2+ 5 is a rational number. 2+ 5 = q p where p,q∈z,q =0 2− q p =− 5
q 2q−p =− 5
⇒− 5 is a rational number ∵ q 2q−p is a rational number But − 5 is not a rational number. ∴ Our supposition 2+ 5 is a rational number is wrong. ⇒2+ 5 is an irrational number.
If possible, let us assume 2+
5
is a rational number.
2+
5
=
q
p
where p,q∈z,q
=0
2−
q
p
=−
5
q
2q−p
=−
5
⇒−
5
is a rational number
∵
q
2q−p
is a rational number
But −
5
is not a rational number.
∴ Our supposition 2+
5
is a rational number is wrong.
⇒2+
5
is an irrational number.
Answer:
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