False. A perfect square trinomial takes the form ( (a - b)^2 = a^2 - 2ab + b^2 ) or ( (a + b)^2 = a^2 + 2ab + b^2 ). The expression ( 16x^2 - 36x + 9 ) can be factored as ( (4x - 3)^2 ), which confirms it is a perfect square trinomial, but it does not fit the specified form ( a^2 - 2ab b^2 ).