SOLUTION: solve for u log3 (u + 18) + log3 (u) = 5

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Question 447944: solve for u
log3 (u + 18) + log3 (u) = 5
Found 2 solutions by stanbon, Alan3354:
Answer by stanbon(75887) About Me  (Show Source):
You can put this solution on YOUR website!
solve for u
log3 (u + 18) + log3 (u) = 5
-------------------
log3[u(u+18)] = 5
----
u^2+18u = 3^5
---
u^2+18u-243 = 0
---
(u-9)(u+27) = 0
---
Positive solution:
u = 9
==========================
Cheers,
Stan H.
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Answer by Alan3354(69443) About Me  (Show Source):
You can put this solution on YOUR website!
log%283%2C%28u+%2B+18%29%29+%2B+log%283%2C%28u%29%29+=+5
log%283%2C%28u%28u+%2B+18%29%29%29+=+5
u%28u+%2B+18%29+=+3%5E5+=+243
u%5E2+%2B+18u+-+243+=+0
(u+27)(u-9) = 0
-27 gives log of neg #s, reject
u = 9