Question

simplify using suitable identity (1.5x +3) (1.5x- 3)

Answer 1

using

(a+b)(a-b)=(a²-b²),

we have
(1.5x)²-(3)²

Answer 2

Here is your answer

$(1.5x + 3)(1.5x - 3) \\ = (1.5x) {}^{2} - (3) {}^{2} \\ = 2.25x {}^{2} - 9 \\ using \: (a + b)(a - b) = a {}^{2} - b {}^{2}$
Hope it helps you