prove that 1/√11 is an irrational number .
Answers
Answer:
So that 1/√11 can be written as p/q, where p, q are coprime integers and q ≠ 0. Here it creates a contradiction that, the LHS p/q is rational while the RHS √11 is irrational. ... Hence our earlier assumption is contradicted and reached the conclusion that √11 is irrational.
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Let us consider 1/
11
be a rational number, then
1/
11
=p/q, where ‘p’ and ‘q’ are integers, $$q \neq 0$$ and p, q have no common factors (except 1).
So,
1/11=p
2
/q
2
q
2
=11p
2
…. (1)
As we know, ‘11’ divides 11p
2
, so ‘11’ divides q
2
as well. Hence, ‘11’ is prime.
So 11 divides q
Now, let q=11k, where ‘k’ is an integer
Square on both sides, we get
q
2
=121k
2
11p
2
=121k
2
[Since, q
2
=11p
2
, from equation (1)]
p
2
=11k
2
As we know, ‘11’ divides 11k
2
, so ‘11’ divides p
2
as well. But ‘11’ is prime.
So 11 divides p
Thus, p and q have a common factor of 11. This statement contradicts that ‘p’ and ‘q’ has no common factors (except 1).
We can say that 1/
11
is
not a rational number.
1/ 11 is an irrational number.
Hence proved.