Solve $LaTeX: \displaystyle 4^{x + 8}=5^{x}$ .

Taking the natural logarithm of both sides gives $LaTeX: \displaystyle (x + 8)\ln(4)=x\ln(5)$ . Distributing gives $LaTeX: \displaystyle 2 x \ln{\left(2 \right)} + 16 \ln{\left(2 \right)} = x \ln{\left(5 \right)}$ . Moving all the $LaTeX: \displaystyle x$ terms to the left hand side and all of the constants to the right side gives: $LaTeX: \displaystyle - x \ln{\left(5 \right)} + x \ln{\left(4 \right)} = - 8 \ln{\left(4 \right)}$ . Factoring out the $LaTeX: \displaystyle x$ gives $LaTeX: \displaystyle x \left(- \ln{\left(5 \right)} + \ln{\left(4 \right)}\right)=- 8 \ln{\left(4 \right)}$ . Isolating $LaTeX: \displaystyle x$ yeilds $LaTeX: \displaystyle x = \frac{- \ln{\left(4 \right)}}{- \ln{\left(5 \right)} + \ln{\left(4 \right)}}$ .