Explanation:
9x² - 36x + 16
= (Ax - B)² = A²x² - 2ABx + B².
By Comparing Coefficients, we have:
A² = 9,
2AB = 36,
B² = 16.
It is obvious that A = 3 and B = 4.
However 2AB = 2(3)(4) = 24 which is not equal to 36.
Hence 9x² - 36x + 16 is not a perfect square trinomial.