that makes things simpler. we now see that its not -no point- now.............so how do we now prove that there are infinitely many of them?
oh! i think it will now be true of all $\displaystyle a /geq 3$, right??? sorry for the later. its a greater than equal to three.....for all integral values of a....
so how do we now prove that there are infinitely many of them?
We don't, can't be done!
There is only one solution: $\displaystyle a=3$.
From other postings you have done, it seems that your textbook has many wrong answers in it.