Changing the subject of an equation.

[Zeeko]

Hello,

Was wondering if anyone could give a little insight into the proper order of functions when rearranging the subject of more complex equations.

For example, I was trying to work out how to make k the subject of this equation:

5k = 7k/(12t) +8t ................................................edited to insert grouping symbols ()

So far I have subtracted 7k/12t from both sides to make sure I isolated the t on the right hand side.

I then multiplied both sides by 12t.

This got me to this stage:

60kt - 7k = 96 t²

I was guessing I would factor next?

Am I heading in the right direction with my working? Does anyone know a good rule of thumb for these type of equations and how best to go about solving them.
Thanks in advance.

 

[Harry_the_cat]

Yes factorise out the \(\displaystyle k\) to get \(\displaystyle k(60t-7)=96t^2\). Then divide both sides by the bracket to get k=....

Note that if you wanted to make \(\displaystyle t\) the subject you would need to write it as
\(\displaystyle 96t^2-60kt +7k=0\) and use the quadratic formula with a=96, b=-60k and c=7k.

 

[JeffM]

Your process was fine. The rule of thumb is to isolate the variable of interest on one side of the equation. After that, it is going to depend on what you have.