Mathematics Stack Exchange is a question and answer site for people studying math at any level and professionals in related fields. It's 100% free, no registration required.

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

I am having trouble with this grade 12 pre-calc question that I am sure will be elementary to most of you. I understand most of it but I do not understand one of the steps.

These are the steps in my answer-key:

$ 4 = log_2x+log_2(x+6) $

$ 4 = log_2(x^2+6x) $

$ 2^4 = x^2+6x $

What happens to 4 to become $2^4$? Thanks!

share|cite|improve this question
Hint: how do you get rid of the $log_2$ on the RHS? Look at laws of logs. – Amzoti Apr 18 '13 at 4:57
up vote 1 down vote accepted

Recall that $$\log_a(b) = y \iff b = a^y$$ In your case, we have $$\log_2(x^2+6x) = 4 \iff x^2+6x = 2^4$$

share|cite|improve this answer

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.