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Question Number 28097 by tawa tawa last updated on 20/Jan/18

lim_(x→∞)   ((3^x  − 2^x )/x^2 )

$$\underset{{x}\rightarrow\infty} {\mathrm{lim}}\:\:\frac{\mathrm{3}^{\mathrm{x}} \:−\:\mathrm{2}^{\mathrm{x}} }{\mathrm{x}^{\mathrm{2}} } \\ $$

Commented by abdo imad last updated on 20/Jan/18

=lim_(x→+∝)   ((3^x (1 −((2/3))^x ))/x^2 )=lim_(x→+∝)   (3^x /x^2 )  =lim_(x→+∝  ) e^(xln3)  e^(−2lnx) = lim_(x→+∝)   e^(x(ln3 −2((lnx)/x)))   =lim_(x→+∝)   e^(xln3) =+∝   because   lim_(x→∝) ((2/3))^x =0  and lim_(x→+∝)   ((lnx)/x)=0 .

$$={lim}_{{x}\rightarrow+\propto} \:\:\frac{\mathrm{3}^{{x}} \left(\mathrm{1}\:−\left(\frac{\mathrm{2}}{\mathrm{3}}\right)^{{x}} \right)}{{x}^{\mathrm{2}} }={lim}_{{x}\rightarrow+\propto} \:\:\frac{\mathrm{3}^{{x}} }{{x}^{\mathrm{2}} } \\ $$$$={lim}_{{x}\rightarrow+\propto\:\:} {e}^{{xln}\mathrm{3}} \:{e}^{−\mathrm{2}{lnx}} =\:{lim}_{{x}\rightarrow+\propto} \:\:{e}^{{x}\left({ln}\mathrm{3}\:−\mathrm{2}\frac{{lnx}}{{x}}\right)} \\ $$$$={lim}_{{x}\rightarrow+\propto} \:\:{e}^{{xln}\mathrm{3}} =+\propto\:\:\:{because}\:\:\:{lim}_{{x}\rightarrow\propto} \left(\frac{\mathrm{2}}{\mathrm{3}}\right)^{{x}} =\mathrm{0} \\ $$$${and}\:{lim}_{{x}\rightarrow+\propto} \:\:\frac{{lnx}}{{x}}=\mathrm{0}\:. \\ $$

Commented by çhëý böý last updated on 20/Jan/18

Good work sir

$${Good}\:{work}\:{sir} \\ $$$$ \\ $$

Commented by tawa tawa last updated on 21/Jan/18

God bless you sir

$$\mathrm{God}\:\mathrm{bless}\:\mathrm{you}\:\mathrm{sir} \\ $$

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