# Limits help

• Nov 11th 2008, 04:15 AM
thelostchild
Limits help
Hi

feeling very stupid here any chance of a push in the right direction with this

$\lim_{x \rightarrow \infty} \frac{5^{n+2}-7^{n+2}}{5^n-7^n}$

any hints would be appreciated

Cheers

Simon :)
• Nov 11th 2008, 04:22 AM
mr fantastic
Quote:

Originally Posted by thelostchild
Hi

feeling very stupid here any chance of a push in the right direction with this

$\lim_{x \rightarrow \infty} \frac{5^{n+2}-7^{n+2}}{5^n-7^n}$

any hints would be appreciated

Cheers

Simon :)

$\frac{5^{n+2}-7^{n+2}}{5^n-7^n} = \frac{5^2 \cdot 5^{n} - 7^2 \cdot 7^{n}}{5^n-7^n} = \frac{5^2 \cdot \left(\frac{5}{7}\right)^{n} - 7^2}{\left(\frac{5}{7}\right)^n - 1} \rightarrow \frac{0 - 49}{0 - 1} = 49$.
• Nov 11th 2008, 04:25 AM
thelostchild
Quote:

Originally Posted by mr fantastic
$\frac{5^{n+2}-7^{n+2}}{5^n-7^n} = \frac{5^2 \cdot 5^{n} - 7^2 \cdot 7^{n}}{5^n-7^n} = \frac{5^2 \cdot \left(\frac{5}{7}\right)^{n} - 7^2}{\left(\frac{5}{7}\right)^n - 1} \rightarrow \frac{0 - 49}{0 - 1} = 49$.

thank you, I really just needed to be shown one like this makes me feel stupid now though!
• Nov 11th 2008, 04:29 AM
mr fantastic
Quote:

Originally Posted by thelostchild
thank you, I really just needed to be shown one like this makes me feel stupid now though!

Better to feel stupid now than in the exam.