Prove that 3 + 2√5 is irrational
Answers
Let 3 + 2√5 be a rational number.
Then the co-primes x and y of the given rational number where (y ≠ 0) is such that:
3 + 2√5 = x/y
Rearranging, we get,
2√5 = (x/y) – 3
√5 = 1/2[(x/y) – 3]
Since x and y are integers, thus, 1/2[(x/y) – 3] is a rational number.
Therefore, √5 is also a rational number. But this confronts the fact that √5 is irrational.
Thus, our assumption that 3 + 2√5 is a rational number is wrong.
Hence, 3 + 2√5 is irrational.
ANSWER
Prove 3+2
5
is irrational.
→ let take that 3+2
5
is rational number
→ so, we can write this answer as
⇒3+2
5
=
b
a
Here a & b use two coprime number and b
=0.
⇒2
5
=
b
a
−3
⇒2
5
=
b
a−3b
∴
5
=
2b
a−3b
Here a and b are integer so
2b
a−3b
is a rational number so
5
should be rational number but
5
is a irrational number so it is contradict
- Hence 3+2
5
is irrational