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 June 11th, 2012, 10:27 AM #1 Newbie   Joined: Jul 2011 Posts: 5 Thanks: 0 How do you know if it is positive or negative infinity? lim -> - inf ((1-x^4)/(x^2+5x))^5 = -inf lim -> inf ((1-x^3)/(x^2+4x))^7 = inf I don't understand how it turns out to be positive or negative infinity. Thanks for the help guys.
 June 11th, 2012, 10:56 AM #2 Math Team   Joined: Nov 2010 From: Greece, Thessaloniki Posts: 1,990 Thanks: 133 Math Focus: pre pre pre pre pre pre pre pre pre pre pre pre calculus Re: How do you know if it is positive or negative infinity? $\lim_{x\to\pm\infty}\left(\frac{1-x^4}{x^2+5x}\right)^{5}=\left(\lim_{x\to\pm\infty} \frac{1-x^4}{x^2+5x}\right)^5=\left(-\infty\right)^{5}=(-1)^5\cdot \left(+\infty\right)=(-1)\cdot\left(+\infty\right)=-\infty$

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