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toadytica305 2 years ago How do you solve when you have logs on one side but not the other? (2 problems inside)

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1. toadytica305

2. mathg8

use the product rule log A + log B = log (AB)

3. toadytica305

I tried that... for Log x + log (x+15) = 2 I have (Log x)(log (x+15)) =2 i dont know what to do after The answer is 5

4. saifoo.khan

\[\lg x(x+15) = 2\]

5. RadEn

convert 2 to log 100

6. AravindG

log x+log (x+15)=log(x(x+15))!!

7. RadEn

it just a hint, so that both sides have log's :)

8. toadytica305

But how do you go from log(x(x+15)=2.. to x=5? I can't get that part

9. RadEn

log(x(x+15))=2 log(x(x+15)=log100 cancel out the log, giving us : x(x+15)=100 or x^2+15x-100=0 solve for x by factorization or by complete square or by quadratic formula

10. RadEn

got it ?

11. toadytica305

Yes! Just solved it.. thank you!

12. RadEn

yw

13. toadytica305

I didn't think of doing log 100 to cancel the logs on both sides

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