if X^4-Y^4 is odd, Which of the following are odd
I X^2-Y^2
II X^2+Y^2
III X^2-2XY+Y^2
Number System
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X^4-Y^4 is odd
Possible scenarios
1. X-Odd, Y-Even
2. X-Even, Y-odd
Condition 1: X^2+Y^2
when X-Odd and Y-Even
X^2 is odd and Y^2 is even
When X-even and Y-odd
X^2 is even and Y^2 is odd
Hence X^2+Y^2 is odd
Same logic applies for X^2-Y^2 also.
Hence X^2+Y^2 is odd
Condition 3: X^2-2XY+Y^2
X^2+Y^2 is always odd and 2XY is always even
Hence X^2-2XY+Y^2 is also odd
Possible scenarios
1. X-Odd, Y-Even
2. X-Even, Y-odd
Condition 1: X^2+Y^2
when X-Odd and Y-Even
X^2 is odd and Y^2 is even
When X-even and Y-odd
X^2 is even and Y^2 is odd
Hence X^2+Y^2 is odd
Same logic applies for X^2-Y^2 also.
Hence X^2+Y^2 is odd
Condition 3: X^2-2XY+Y^2
X^2+Y^2 is always odd and 2XY is always even
Hence X^2-2XY+Y^2 is also odd