Question 1044562
The equation which the website shows is based on the formula for Difference Of Cubes.  You can find the formula yourself using polynomial division.
Something is missing in what the website tells you.  You have found a mistake.


Look:  {{{x^3-y^3=(x-y)(x^2+xy+y^2)}}}



Maybe I have not understood some of what YOU wrote?
Did you mean,  {{{3a-(1/2)a=7}}}
or did you mean, {{{3a-1/(2a)=7}}}
?


The way that {{{3/2}}} becomes one of the terms in one of the polynomial sum-of-terms factors is therefore becoming more obvious.