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Q5Section A (Section A)5 of 15

Continuity and partial derivatives at a point for an oscillating function of two variables

Let

f(x,y)={x2+y2 sin⁡(1x2+y2),(x,y)≠(0,0), 0,(x,y)=(0,0).f(x,y)=\begin{cases}\sqrt{x^2+y^2}\,\sin\left(\dfrac1{\sqrt{x^2+y^2}}\right), & (x,y)\ne(0,0),\ 0, & (x,y)=(0,0).\end{cases}

Then at the point (0,0)(0,0),

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