\(\left(2x-3\right)^2-2\left(4x^2-9\right)+\left(2x+3\right)^2\\ =\left(2x-3\right)^2-2\left(2x-3\right)\left(2x+3\right)+\left(2x+3\right)^2\\ =\left[\left(2x-3\right)-\left(2x+3\right)\right]^2\\ =\left(2x-3-2x-3\right)^2\\ =\left(-6\right)^2\\ =36\)