You first get the equation in this form with the  positive:



then you substitute in this

 

Then you simplify and you get two answers, one using the + and
one using the -.

Example:



Write it in descending order on the left with only 0 on the right:



Multiply through by -1 to make the first term  positive:





Now simplify:







The two solutions are:

 and 

You can get the approximate decimal values with a calculator:

  and 

Edwin