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Algebra
Logarithms
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Solve \(\displaystyle \log_{ 10 }(x + 15) + \log_{ 10 }(x + 1005) = 4\)

Using the product rule for logarithms gives \(\displaystyle \log_{ 10 }(\left(x + 15\right) \left(x + 1005\right)) \) and rewriting in exponential form gives \(\displaystyle \left(x + 15\right) \left(x + 1005\right) = 10000\) expanding and setting the equation equal to zero gives \(\displaystyle x^{2} + 1020 x + 5075 = 0\). Factoring gives \(\displaystyle \left(x + 5\right) \left(x + 1015\right)=0\). This gives two possible solutions \(\displaystyle x=-1015\) or \(\displaystyle x=-5\). \(\displaystyle x=-1015\) is an extraneous solution. The only soution is \(\displaystyle x=-5\).

Download \(\LaTeX\) 

\begin{question}Solve $\log_{ 10 }(x + 15) + \log_{ 10 }(x + 1005) = 4$
    \soln{10cm}{Using the product rule for logarithms gives $\log_{ 10 }(\left(x + 15\right) \left(x + 1005\right)) $ and rewriting in exponential form gives $\left(x + 15\right) \left(x + 1005\right) = 10000$ expanding and setting the equation equal to zero gives $x^{2} + 1020 x + 5075 = 0$.  Factoring gives $\left(x + 5\right) \left(x + 1015\right)=0$. This gives two possible solutions $x=-1015$ or $x=-5$. $x=-1015$ is an extraneous solution.  The only soution is $x=-5$. }

\end{question}

Download Question and Solution Environment\(\LaTeX\)
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HTML for Canvas 
<p> <p>Solve  <img class="equation_image" title=" \displaystyle \log_{ 10 }(x + 15) + \log_{ 10 }(x + 1005) = 4 " src="/equation_images/%20%5Cdisplaystyle%20%5Clog_%7B%2010%20%7D%28x%20%2B%2015%29%20%2B%20%5Clog_%7B%2010%20%7D%28x%20%2B%201005%29%20%3D%204%20" alt="LaTeX:  \displaystyle \log_{ 10 }(x + 15) + \log_{ 10 }(x + 1005) = 4 " data-equation-content=" \displaystyle \log_{ 10 }(x + 15) + \log_{ 10 }(x + 1005) = 4 " /> </p> </p>
HTML for Canvas
<p> <p>Using the product rule for logarithms gives  <img class="equation_image" title=" \displaystyle \log_{ 10 }(\left(x + 15\right) \left(x + 1005\right))  " src="/equation_images/%20%5Cdisplaystyle%20%5Clog_%7B%2010%20%7D%28%5Cleft%28x%20%2B%2015%5Cright%29%20%5Cleft%28x%20%2B%201005%5Cright%29%29%20%20" alt="LaTeX:  \displaystyle \log_{ 10 }(\left(x + 15\right) \left(x + 1005\right))  " data-equation-content=" \displaystyle \log_{ 10 }(\left(x + 15\right) \left(x + 1005\right))  " />  and rewriting in exponential form gives  <img class="equation_image" title=" \displaystyle \left(x + 15\right) \left(x + 1005\right) = 10000 " src="/equation_images/%20%5Cdisplaystyle%20%5Cleft%28x%20%2B%2015%5Cright%29%20%5Cleft%28x%20%2B%201005%5Cright%29%20%3D%2010000%20" alt="LaTeX:  \displaystyle \left(x + 15\right) \left(x + 1005\right) = 10000 " data-equation-content=" \displaystyle \left(x + 15\right) \left(x + 1005\right) = 10000 " />  expanding and setting the equation equal to zero gives  <img class="equation_image" title=" \displaystyle x^{2} + 1020 x + 5075 = 0 " src="/equation_images/%20%5Cdisplaystyle%20x%5E%7B2%7D%20%2B%201020%20x%20%2B%205075%20%3D%200%20" alt="LaTeX:  \displaystyle x^{2} + 1020 x + 5075 = 0 " data-equation-content=" \displaystyle x^{2} + 1020 x + 5075 = 0 " /> .  Factoring gives  <img class="equation_image" title=" \displaystyle \left(x + 5\right) \left(x + 1015\right)=0 " src="/equation_images/%20%5Cdisplaystyle%20%5Cleft%28x%20%2B%205%5Cright%29%20%5Cleft%28x%20%2B%201015%5Cright%29%3D0%20" alt="LaTeX:  \displaystyle \left(x + 5\right) \left(x + 1015\right)=0 " data-equation-content=" \displaystyle \left(x + 5\right) \left(x + 1015\right)=0 " /> . This gives two possible solutions  <img class="equation_image" title=" \displaystyle x=-1015 " src="/equation_images/%20%5Cdisplaystyle%20x%3D-1015%20" alt="LaTeX:  \displaystyle x=-1015 " data-equation-content=" \displaystyle x=-1015 " />  or  <img class="equation_image" title=" \displaystyle x=-5 " src="/equation_images/%20%5Cdisplaystyle%20x%3D-5%20" alt="LaTeX:  \displaystyle x=-5 " data-equation-content=" \displaystyle x=-5 " /> .  <img class="equation_image" title=" \displaystyle x=-1015 " src="/equation_images/%20%5Cdisplaystyle%20x%3D-1015%20" alt="LaTeX:  \displaystyle x=-1015 " data-equation-content=" \displaystyle x=-1015 " />  is an extraneous solution.  The only soution is  <img class="equation_image" title=" \displaystyle x=-5 " src="/equation_images/%20%5Cdisplaystyle%20x%3D-5%20" alt="LaTeX:  \displaystyle x=-5 " data-equation-content=" \displaystyle x=-5 " /> . </p> </p>