Thursday 7 March 2013

calculus - The limit of this function as x approaches 2 from the positive direction (the right).




$$ \lim_{x \rightarrow 2}\frac {\sqrt{x^2-4}}{x-2}$$




Am I correct in thinking the limit does not exist? Since as x approaches 2 from the right the function increases to infinity and a limit cannot equal infinity. Thanks!


Answer




$$\lim_{x\rightarrow 2^+} \frac{\sqrt{x^2-4}}{x-2}=\lim_{x\rightarrow 2^+}\frac{\sqrt{(x-2)(x+2)}}{x-2}=\lim_{x\rightarrow 2^+}\frac{\sqrt{(x-2)}\sqrt{(x+2)}}{x-2}=\lim_{x\rightarrow 2^+}\frac{\sqrt{(x+2)}}{\sqrt{(x-2)}}$$



Then as you said the denominator tends to $0^+$ and hence the whole limit tends to $+\infty$


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