No because it would be
if you knew that
ax^2+bx+c was a trinomial square, then the factored form would be
or 
so
if w^2-9w+81 is perfect square, factored form is either
or 
aka 
or 
expand them
(x+9)^2=x^2+18x+81, wron middle term
(x-9)^2=x^2-18x+81 wrong
so it is not
if you knew that
ax^2+bx+c was a trinomial square, then the factored form would be
so
if w^2-9w+81 is perfect square, factored form is either
expand them
(x+9)^2=x^2+18x+81, wron middle term
(x-9)^2=x^2-18x+81 wrong
so it is not