So the quadratic equation is
[tex]4n^2-81=0 \\ 4n^2=81 \\ n^2= \frac{81}{4} [/tex]
We can have two values for n which is either the positive or negative squareroot of 81/4
[tex]n= \frac{9}{2} \\ n=- \frac{9}{2} [/tex]
We can also factor is out:
[tex]4n^2-81=(2n+9)(2n-9)[/tex] and we get the same answer
