Because m > 1 2m + 1\ge 4 So 2^{2m+1} is divisible by 16.
2^{2m+1} is double of (2^m)^2 and is not a square.
Now we consider 2 cases
Let us consider when n is odd
Then n= (2k+1)
So n^2 = (2k+1)^2 = 4k^2 + 4k + 1 = 4k(k+1)+1
Ss k or k+1 is even we n^2 \equiv 1 \pmod 8
So 2^{2m+1} is divisible by 8 and minimum number above n^2 which is divisible by 8 is n^2 + 7
So we have proved for the case n is odd.
Let us consider when n is even
If n^2 is divisible by 8 then n^2 is divisible by 16 and as 2^{2m+1} is divisible by 16 and n^2 is divisible by 16
So 2^{2m+1}-n^2 = 16k for some positive k
So 2^{2m+1}-n^2 \ge16
Hence 2^{2m+1}-n^2 \gt 7 or 2^{2m+1} \gt n^2+ 7
If n^2 is even and is not divisible by 8 then n is of the form 4k+2
n^2= 16k^2 + 16k + 4
Or n^2 \equiv 4 \pmod {16}
As 2^{2m+1} = 0 \pmod {16}
So 2^{2m+1} \ge n^2 + 12
Hence 2^{2m+1} \gt n^2 + 7
we have proved for all 3 cases hence done
No comments:
Post a Comment