00:01
Given that x is even, so x can be expressed as x equal to 2k and y is odd.
00:09
So, y is equal to 2k plus 1.
00:13
So now we have to prove whether x squared plus y square is odd or even.
00:19
So, let's see.
00:22
So substituting the values of x and y from here, x squared plus y square would become 2k whole square plus 2k plus 1 whole 1 whole square that gives us 4k square plus 4k square plus 4k plus 1.
00:40
I just expanded a plus b whole square to here.
00:44
So that gives us 8k square plus 4k plus 1.
00:50
And we know that any number which is multiplied by a 2 would be an even number.
00:56
So 8 can be represented as 2 into 4k square.
01:03
Plus 4k can be represented as 2 into 2k plus 1.
01:08
So this is an even number, this is an even number.
01:12
So this whole thing can be represented as an even number, which is, let's say, 2l plus 1.
01:21
So that gives us that x squared plus y square is indeed an odd number.
01:29
So that's also the first part of the question.
01:33
Let's see the second part.
01:34
So we are given that x and y are rational numbers.
01:39
So x and y are rational numbers...