Giúp tớ câu này với: Tìm lim->0 (ln(cos(x))/x^2

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\(\lim\limits_{x\to0}\dfrac{In(cosx)}{x^2}\\=\lim\limits_{x\to 0}\dfrac{In(cosx)'}{(x^2)'}\text{(quy tắc l'hospital)}\\=\lim\limits_{x\to 0}\dfrac{\dfrac{(cosx)'}{cosx}}{2x}\\=\lim\limits_{x\to 0}\dfrac{\dfrac{-sinx}{cosx}}{2x}\\=-\dfrac{1}{2}.\lim\limits_{x\to 0}\dfrac{sinx}{x}.\lim\limits_{x\to0}\dfrac{1}{cosx}\\=-\dfrac{1}{2}.1.\dfrac{1}{cos0}\\=-\dfrac{1}{2}.\)

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