Solution for this Logarithmic Equation Recently I was going through a problem from the book Problems in Mathematics - *V Govorov & P Dybov* . (x-2)^(log^2(x-2)+log(x-2)^5-12)=10^2log(x-2) I tried solving by first considering log(x−2) as a variable, say t. Then I expressed (x−2) as 10^t . Then after using some properties of log, I reached till here- 10^(t^3+5t^2-12t)=10^2t or 10^(t^3+5t^2-12t-2)=t Now I have no idea how to approach further. The answer in the references says x=3,102,2+10^(−7)
Marisol Rivers
Answered question
2022-07-21
Solution for this Logarithmic Equation Recently I was going through a problem from the book Problems in Mathematics - *V Govorov & P Dybov* .
I tried solving by first considering as a variable, say . Then I expressed as . Then after using some properties of log, I reached till here-
or
Now I have no idea how to approach further. The answer in the references says
Answer & Explanation
Sandra Randall
Beginner2022-07-22Added 17 answers
Equations such as
cannot be solve using analytical methods and numerical methods, such as Newton, should be used. As you probably notice, you are looking for the intersection of two curves, namely
If you plot the functions on the same graph, you should notice a clear intersection around . There is also a root close to since, around this value, a Taylor expansion gives
which has a negative slope while has a positive slope. Using this expansion gives another estimate close to
So, let us define the overall function
and let us try to find its roots starting from a given estimate . Newton procedure will update this guess accodring to
For the first solution, let us start at ; Newton iterates are then : , , which is the solution for six significant figures. For the second solution, let us start at ; Newton iterates are then : , , which is again the solution for six significant figures. Since, from your changes of variable , the solutions are then and which are the values given by Tunococ.