Let f: R2R where f(x, y) = x² + y² if both x and y are rational and f(x, y) = 0 otherwise. Prove that Df(0, 0) exists. Note: Df(c) only exists at c = (0,0) and f is continuous only at (0,0).

Advanced Engineering Mathematics
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ISBN:9780470458365
Author:Erwin Kreyszig
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Chapter2: Second-order Linear Odes
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Real Analysis II
Let \( f: \mathbb{R}^2 \to \mathbb{R} \) where \( f(x, y) = x^2 + y^2 \) if both \( x \) and \( y \) are rational and \( f(x, y) = 0 \) otherwise. Prove that \( Df(0,0) \) exists. Note: \( Df(c) \) only exists at \( c = (0,0) \) and \( f \) is continuous only at \( (0,0) \).
Transcribed Image Text:Let \( f: \mathbb{R}^2 \to \mathbb{R} \) where \( f(x, y) = x^2 + y^2 \) if both \( x \) and \( y \) are rational and \( f(x, y) = 0 \) otherwise. Prove that \( Df(0,0) \) exists. Note: \( Df(c) \) only exists at \( c = (0,0) \) and \( f \) is continuous only at \( (0,0) \).
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