I used the method of contradiction by assuming that √2 is a rational number. Then, by the definition of rational number, there exist two integers p and q whose ratio equals √2. Thus,
pq=√2
Squaring both sides,
p2/q2=2
or p2=2q2
This means that p2 is an even number, implying that p is even.
Now, any even integer can be written as 2kf where f is any odd integer and k is some positive integer (the minimum value of k and f is 1 since even numbers start from 2=21⋅1). For odd numbers, k=0.
For example, 8=23⋅1, 4=22⋅1, 18=21⋅9, 24=23⋅3, −12=22⋅(−3), etc.
Now, from (b), q2 can be even or odd.
Case 1: q2 is even (thus meaning q is even). Then p=2k1⋅f1 (say) and q=2k2∗f2 (say). Note here in this case, both conditions k1=k2 and f1=f2 can't hold simultaneously since that would mean p/q=1 and here p/q=√2 (from (x))). Let's consider the condition when k1=k2=k but f1≠f2. Then
p2q2=(2kf1)2(2kf2)2=f21f22=2
(from (a)), i.e.: odd/odd (f1 and f2 are odd) can never equal 2.
Now lets consider f1=f2=f but k1≠k2, thus (2k1f)2/(2k2f)2=22(k1−k2)=2 meaning k1−k2=0.5 but k1,k2 are integers, so their difference can't be 0.5. (Also here, k1−k2 must be greater or equal to 1 since 2k1−k2=√2, k1−k2 can't be negative since √2>1, but k1−k2≥1 can't satisfy (a) since the minimum value of p/q in this case will be 2 which is surely greater than √2.)
Now lets consider f1≠f2 and k1≠k2, thus (2k1f1)2(2k2f2)2=22(k1−k2)f21f22 can never equal 2 since f21f22 is either odd or "odd/odd" ie: it doesn't contain 2 as a factor and 22(k1−k2) is a power of 2. So in 22(k1−k2)f21f22, there's no chance of cancellation of the odd factor f21f22.
Case 2: q2 is odd (thus meaning q is odd). q=f′ (say, here k=0 for q but not for p), thus from (a) 22kf2f′2=2 but this isn't possible since a power of 2 multiplied with odd factor can't equal 2.
Thus, both case 1 and 2 suggest that for any possible combination of k1,k2,f1 and f2, p/q≠√2, i.e.: for no value of integers p and q, p/q=√2. Thus, this contradicts our assumption that √2 is rational. Therefore it must be irrational.
PLS NOTE that i would like to clarify that f21/f22 is either an odd integer or a fraction of odd/odd or 1/odd form, thus not containing 2 as a factor,for any 2n, if it has to be reduced to 2 , must be multiplied with 1/2(n−1) but f21/f22 can't be of 1/2[n−1] form since for odd nos, in 2k*f notation, k is 0 , so 2 vanishes as 2k becomes 1 in this case thus f1/f2 can't be represented as 1/ 2(n−1) in which n has to be existent.
therefore 22(k1−k2)f21f22 can never equal 2 as to further explain the 3rd condition of case 1
Difficulty: is my approach correct? This proof which I thought is different
from proofs found on the internet or books since I have used p and q as any integers, which may have a common factor. So I am not sure if I am on right track. Will someone please check this out and make kind comments?
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