properties of logs
http://dwb4.unl.edu/Chem/CHEM869R/CHEM869RMats/Logs/Logs.html
http://academics.utep.edu/Portals/1788/CALCULUS%20MATERIAL/3_3_4%20PROPERTIES%20OF%20LOGS.pdf
http://home.windstream.net/okrebs/page56.html
https://www.khanacademy.org/math/trigonometry/exponential_and_logarithmic_func/log_functions/v/solving-logarithmic-equations_DUP_1
http://academics.utep.edu/Portals/1788/CALCULUS%20MATERIAL/3_3_4%20PROPERTIES%20OF%20LOGS.pdf
http://home.windstream.net/okrebs/page56.html
https://www.khanacademy.org/math/trigonometry/exponential_and_logarithmic_func/log_functions/v/solving-logarithmic-equations_DUP_1