Solving Equations with Log Terms and Other
Terms
Example
Solve: log5 (5x + 10) - 1 = log5 25.
Solution |
|
log5 (5x + 10) - 1 = log5
25 |
Step 1 |
Rewrite the equation with the logs
on one side and the constant term
on the other side.
To make the calculations easier,
rewrite the equation so the constant
term is positive.
Add 1 to both sides.
Subtract log525 from both sides. |
log5 (5x + 10) = log5
25 + 1 log5 (5x + 10)
- log5 25 = 1 |
Step 2 |
Combine the logs into a
single log.
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|
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Use the Log of a Quotient Property. |
|
Step 3 |
Convert the equation to exponential
form and solve.
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|
|
Convert to exponential form. Factor numerator and denominator.
Cancel the common factor of 5.
|
|
|
Multiply both sides by the LCD, 5.
Subtract 2 from both sides. |
25 = x + 2
23 = x |
So, the solution is x = 23.
Note:
Here is a check of the solution:
Is Is
Is
Is
Is
Is |
log5 (5x + 10) -
1 log5 (5
· 23 + 10) - 1
log5 (125) - 1
log5 (53) - 1
3 - 1
2 |
= log5 25
= log5 25
= log5 25
= log5 52
= 2
= 2 |
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? Yes |
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