Saturday, 31 March 2018

calculus - what about $limlimits_{xto0}-frac{sin x}x=$?



we all know that:



$\lim\limits_{x\to0}\frac{\sin x}x=1$



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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