Sunday, April 14, 2019

limits - Which function grows faster?



Which function grows faster



𝑓(𝑛)=2𝑛2+3𝑛 and 𝑔(𝑛)=2𝑛+1



by using the limit theorem I will first simplify




then I will just get lim



Is this enough?
I say it will go then to infinity so the f(n) is growing faster? I am asking this question because I have to find it by using limit but I didn't need to use l'hopital rule!


Answer



Before Edit:
Your idea was correct, but you didn’t simplify the limit properly.
\lim_{n \to \infty} \frac{2^{n^2+3n}}{2^n+1}
It is enough to divide both the numerator and denominator by 2^n.

\lim_{n \to \infty} \frac{\frac{2^{n^2+3n}}{2^n}}{\frac{2^n+1}{2^n}} = \lim_{n \to \infty} \frac{2^{n^2+3n-n}}{2^{n-n}+\frac{1}{2^n}} = \lim_{n \to \infty} \frac{2^{n^2+2n}}{1+\frac{1}{2^n}}
As n \to \infty, it becomes clear that the limit tends to \infty since the numerator tends to \infty while the denominator tends to 1.



After Edit: Yes, your way is correct.


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