Saturday, 31 March 2018

calculus - what about limlimitsxto0fracsinxx=?



we all know that:



lim



so what is the negative




\lim\limits_{x\to0}-\frac{\sin x}x=?



i am trying to prove what about \lim\limits_{x\to0}\frac{x^2\sin \frac 1x}{\sin^2 x}



i got to \frac{-x^2}{\sin^2 x} \le \frac{x^2\sin \frac 1x}{\sin^2 x}\le\frac{x^2}{\sin^2 x}



and \lim\limits_{x\to0}\frac{x^2}{\sin^2 x}= \lim\limits_{x\to0}\frac{\sin x}x\lim\limits_{x\to0}\frac{\sin x}x= 1\times1=1



and\lim\limits_{x\to0}-\frac{x^2}{\sin^2 x}= \lim\limits_{x\to0}\frac{\sin x}x\lim\limits_{x\to0}-\frac{\sin x}x=?



Answer



Simply put,




\lim_{x\to a} (Af(x))=A\lim_{x\to a} f(x),\text{ where $A$ is a constant.}
So let A=-1 in your expression.




Edit: Let me generalize:




If \lim_{x\to a}f(x),\lim_{x\to a}g(x) exist, then \lim_{x\to a}(f(x)g(x)) exists. So, let g(x)=\dfrac{\sin x}{x},f(x)=-1.


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