# Logarithms

• Mar 18th 2010, 02:18 PM
Alan306090
Logarithms
How do you do

Log base 5 of (x ^2 + x + 4) = 2?
• Mar 18th 2010, 02:21 PM
skeeter
Quote:

Originally Posted by Alan306090
How do you do

Log base 5 of (x ^2 + x + 4) = 2?

first, change it to an exponential equation ... you'll get a quadratic to solve.

don't forget to check your solutions in the original log equation for domain issues.
• Mar 18th 2010, 02:28 PM
Alan306090
Quote:

Originally Posted by skeeter
first, change it to an exponential equation ... you'll get a quadratic to solve.

don't forget to check your solutions in the original log equation for domain issues.

25 = x ^2 + x + 4

0 = x^2 +x -21

then what? I can't factor it
• Mar 18th 2010, 02:52 PM
pickslides
Quote:

Originally Posted by Alan306090
25 = x ^2 + x + 4

0 = x^2 +x -21

then what? I can't factor it

$x = \frac{-b\pm\sqrt{1^2-4\times 1\times -21}}{2\times 1}=\dots$