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4 Answers

log(2x+1)=1+log(x-2)

I am assuming these are common logarithms, where the base is 10.

log(10) = 1

log(2x+1)=log(10) + log(x-2)

The sum of logs (of the same base) is the log of the product.

log(2x+1) = log[10(x-2)] = log(10x-20)

Remove the log from left and right.

2x+1 = 10x-20

Move all terms with the x to the left side and all other terms to the right side.  Remember to switch signs when you switch sides.

2x-10x = -20 - 1

-8x = -21

x = 21/8

Now go back and make sure it works with each of the logs in the original questions.  The parameter to a log can not be negative.

log(2x+1) = log(2(21/8)+1) = log(21/4+1) = log(25/4)

The argument is positive, so this is fine.

log(x-2) = log(21/8-2) = log(21/8-16/8) = log(5/8)

This is still positive.  So this x=21/8 works for all logs, therefore it is a valid answer.
by Level 1 User (350 points)
lim (h-0) [{log(1+2h)-2log(1+h)}/h2
by
log(2x+1)=1+log(x-2) 2x+1=1(x-2) 2x-x=-2-1 x=-3
by Level 4 User (7.5k points)
I must point out that it is impossible to take a log of a negative number, so your answer cannot be valid.
log(2x + 1) = 1 + log(x - 2)
log (2(-3) + 1) = 1 + log((-3) - 2)
log(-6 + 1) = 1 + log(-3 - 2)
log(-5) = 1 + log(-5)
There is a negative arguement for the log on both sides.
Both sides are invalid.
log(2x+1) = 1 + log(x-2)

- log(x-2)         - log(x-2)

------------------------------------------

log(2x+1) - log(x-2) = 1

log((2x+1)/(x-2)) = 1

10 = (2x+1)/((x-2)

10(x-2) = 2x+1

10x - 20 = 2x +1

-2x +20     -2x +20

----------------------------

8x = 21

x = 21/8
by Level 8 User (36.8k points)
edited by

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