Write down the logarithmic equation. Move all terms with logarithms to one side and all constants (plain numbers not attached to variables or logarithms) to the other. For instance, "log(2X) -3 = 6 - log(4)" would become "log(2X) + log(4) = 6 + 3".
Combine any plain numbers such as 6 or 10. Then, use logarithmic properties to combine the logarithms into one. If the logarithms are being added, they turn into one logarithm with their insides multiplied and if they are being subtracted, they turn into one logarithm with their insides divided. For example, log(2X) + log(4) = 6 + 3 turns into log(6X) = 9.
Set the equation equal to zero so the constant is back on the same side as the logarithm and you can find the answers by then solving for the intercepts. "Log(6X) = 9" becomes "log(6X) - 9 = 0".
Turn on the TI-83 Plus with the "ON" button in the lower left corner of the calculator keyboard. Then press the "Y=" button in the upper left corner. Type in the left side of the equation, then press "GRAPH" in the upper right corner to display the graph of the equation.
Hit the "2nd" button and then the "TRACE" button in the middle of the top row of keys. Use the arrow buttons to scroll down to "ZERO" and press "ENTER" in the lower right corner to select it.
Trace the line of the graph just to the left of where it crosses the X-axis using the arrow keys. Press "ENTER." Then, trace the graph to the other side of the axis and press "ENTER" a second and third time. The answer to the equation is displayed on the bottom of the screen after the "x=".
Repeat Steps 5 and 6 for any other places the graph appears to cross the X-axis.