Step 1: Apply the logarithm property lna+lnb=ln(ab).
The given equation is:
ln(x+3)+ln(x+5)=ln15
Using the property, we combine the terms on the left side:
ln((x+3)(x+5))=ln15
Step 2: Equate the arguments of the logarithms.
Since the natural logarithm is a one-to-one function, if lnA=lnB, then A=B.
(x+3)(x+5)=15
Step 3: Expand and solve the quadratic equation.
Expand the left side:
x2+5x+3x+15=15
x2+8x+15=15
Subtract 15 from both sides:
x2+8x=0
Factor out x:
x(x+8)=0
This gives two potential solutions:
x=0orx+8=0⟹x=−8
Step 4: Check the validity of the solutions based on the domain of the natural logarithm.
For ln(x+3) to be defined, x+3>0⟹x>−3.
For ln(x+5) to be defined, x+5>0⟹x>−5.
Both conditions must be satisfied, so we need x>−3.
Let's check our potential solutions:
• For x=0:
0>−3. This condition is satisfied.
Substituting x=0 into the original equation: ln(0+3)+ln(0+5)=ln3+ln5=ln(3×5)=ln15. This is correct. So, x=0 is a valid solution.
• For x=−8:
−8>−3. This condition is NOT satisfied.
Substituting x=−8 into the original equation would give ln(−8+3)=ln(−5) and ln(−8+5)=ln(−3), which are undefined in the set of real numbers. So, x=−8 is not a valid solution.
Therefore, the only valid solution is x=0.
Step 5: Select the correct option.
Based on our analysis, the correct option is A.
The final answer is A)x=0only.
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