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Show that square of any odd …

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Show that square of any odd positive integer is in form 4m+1 for some integer m
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Sia ? 6 years, 6 months ago

Let a be any odd positive integer, then on dividing a by b, we have

 a = bq+r,{tex}​​​​0 \leqslant r < b{/tex}.....(i) [by Euclid's division lemma]

On putting b = 2 in Eq.(i), we get

 a = 2q+r, {tex}0\leqslant r < 2{/tex}
 ⇒  r = 0 or 1

If r = 0, then a = 2q, which is divisible by 2. So, 2q is even.

If {tex}r = 1{/tex}, then {tex}a = 2q + 1{/tex}, which is not divisible by 2. So {tex}(2q+1){/tex} is odd.

Now, as a is odd, so it cannot be of the form 2q.
Thus, any odd positive integer a is of the form (2q+1).

Now, consider a2 = (2q+1) = 4q+ 1 + 4q  {tex}\lbrack\therefore(x+y)^2=x^2+y^2+2xy\rbrack{/tex}

= 4( q+ q ) + 1 = 4m + 1, where m = q2 + q

Hence, for some integer m, the square of any odd integer is of the form 4m+1.

Hence Proved.

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