MIT grad shows how to solve log equations, using LOG PROPERTIES to simplify and solve. More videos with Nancy coming in 2017! To skip ahead: 1) For solving BASIC LOG EQUATIONS, skip to 0:22. 2) For ONE LOG ON EACH SIDE (EQUALITY property), skip to 2:36. 3) For TWO LOGS ADDED together and equaling a number (PRODUCT property), skip to 5:25. 4) For MANY LOGS, SUBTRACTED and ADDED, and using the QUOTIENT property, POWER property, and the other properties, skip to 9:53.
For my video on logarithm basics like how to EVALUATE LOGS, including natural logs (ln x), jump to: https://youtu.be/ZIwmZ9m0byI
SOLVING LOGARITHMIC EQUATIONS: Every logarithm is connected to an exponential form. The best way to figure out a log is to REARRANGE THE LOG INTO EXPONENTIAL FORM and then solve for x. I show a quick recap of how to rewrite a log into exponential form, but for a longer explanation of rearranging into exponential form to evaluate a log, jump to my video "Logarithms... How?" (https://youtu.be/ZIwmZ9m0byI). In this video, I show you more complicated log equations with more than one log, where you'll need the LOG PROPERTIES to simplify and be able to condense down to one logarithm on a side so that you can solve. If you have one log on each side of the equation, with the same base, you can use the EQUALITY PROPERTY. If you have more than one log on a side of the equation (with the same base), you can use the PRODUCT PROPERTY (if the logs are added) or the QUOTIENT PROPERTY (if the logs are subtracted) to combine the logs into one log. If you have a number multiplied in front of a log, as a coefficient, you can use the POWER PROPERTY to bring the coefficient up as a power inside the log argument. Once you simplify the log equation using the product, quotient, and/or power properties, you can either 1) solve by using the equality property if you just have one log on each side (with same base), or 2) solve by rewriting into exponential form if you have a log on one side and a number on the other side. IMPORTANT: You have to CHECK your solutions for log equations. Any numbers you get as solutions you have to plug back into the original equation to check. If a solution does not work or gives an undefined value, then it is an "extraneous solution" and must be thrown out!
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