Tuesday, 2 April 2019

calculus - Why does the following limit give two answers?

I want to calculate



$$ \lim_{t \to 0} \frac{t^2}{\sin^2(t)}$$



and I proceed as follows



$$\stackrel{H}{=} \lim_{t \to 0} \frac{2t}{2\sin(t)\cos(t)} \implies \lim_{t \to 0} \frac{2t}{\sin(2t)}$$




and when evaluated gives



$$\stackrel{H}{=} \lim_{t \to 0} \frac{2}{2\cos^2(t)-2\sin^2(t)} =1$$



But evaluating the other equivalent term gives



$$\stackrel{H}{=} \lim_{t \to 0} \frac{2}{2\sin(2t)\cos(2t)} $$



and that does not exist as the left hand and right hand limits are not equal.




So, what do you think?

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