Prove $\lim_{(h,k)\to 0} \dfrac{|f(h,k)|}{|(h,k)|}=0$ for bilinear $f$

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I have posted the problem 2.12 from Spivaks calculus on Manifolds below along with a solution for it. Before looking at this solution, I attempted to prove it by writing this

$\lim_{(h,k)\to 0} \dfrac{|f(h,k)|}{|(h,k)|} \leq \lim_{(h,k)\to 0} \dfrac{M|(h,k)|^2}{|(h,k)|}$ for some $M>0$

because earlier there was a question asking


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And to continue the proof we can now write

$\lim_{(h,k)\to 0} M|(h,k)| = 0$

Does this proof work?

And here is he problem along with the solution

Thanks

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Solution

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