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## clarkjets 2 years ago logs question

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1. clarkjets

|dw:1358409590944:dw|

2. RolyPoly

\[\log_3(x+4)+\log_3(x-2)=3\]log a + log b = log (ab) \[\log_3(x+4)(x-2)=3\] (x+4)(x-2) = 3^3

3. clarkjets

so would it be x^2+2x-17=0 which makes the roots x = {3.243, -5.243}?

4. RolyPoly

Not quite, can you check again?

5. clarkjets

I'm sorry I can't seem to find where im going wrong

6. RolyPoly

The equation you got was wrong..

7. RolyPoly

(x+4)(x-2) = 3^3 x^2 + 2x - 8 - 3^3 =0 ^Simplify this

8. clarkjets

is it not x^2+2x-17 ?

9. RolyPoly

what is 3^3?

10. clarkjets

oh my apologies I was thing of multiplying, so it is x^2+2x+19?

11. RolyPoly

Hmmm... x^2 + 2x - 8 - 3^3 =0

12. clarkjets

x^2+2x-35=0 ?

13. RolyPoly

Yup :) Now, solve it~

14. clarkjets

x=5 and x=-7 ?

15. RolyPoly

Yes, but you have to reject one answer there.

16. RolyPoly

You cannot take log for a negative number.

17. clarkjets

-7 correct?

18. clarkjets

ok thank you so much

19. RolyPoly

You're welcome :)

20. RolyPoly

And yes, you need to reject -7 :)

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