Let u(r, ) = r 2 cos 2 . Use Eq. (8) to compute u 2 . Then compute u 2 directly by observing that

Let u(r, θ) = r² cos² θ. Use Eq. (8) to compute ΙΙ∇uΙΙ². Then compute ΙΙ∇uΙΙ² directly by observing that u(x, y) = x², and compare.

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