a)
2x(x-3) - 2x^2 = 12
Expanding the left side:
2x^2 - 6x - 2x^2 = 12
Combining like terms:
-6x = 12
Dividing by -6:
x = -2

b)
(2-x)(x+2) - x(1-x) = -3
Expanding the left side:
2x + 4 - x^2 - 2x - x^2 = -3
Combining like terms:
-2x - 2x - 2x^2 = -3
-4x - 2x^2 = -3
Rearranging:
2x^2 + 4x - 3 = 0
Solving the quadratic equation:
x = -3 or x = 1/2

c)
x(2x-40+x(3-2x)-2) = 0
Expanding the left side:
2x^2 - 40x + 3x^2 - 2x - 2x = 0
Combining like terms:
5x^2 - 42x = 0
Factor out x:
x(5x - 42) = 0
Setting each factor to zero:
x = 0 or x = 42/5

d)
(9x-2)(9x+1) - (x^2 + 2x) = 3
Expanding the left side:
81x^2 + 9x - 18x - 2 - x^2 - 2x = 3
Combining like terms:
80x^2 - 11x - 2 = 3
Rearranging:
80x^2 - 11x - 5 = 0
This is a quadratic equation that can be solved using the quadratic formula.