Giải phương trình:

a) \(x^3-3x^2-9x+12=0\)

b) \(\left(x-3\right)^4+\left(x+1\right)^4=82\)

c) \(x^4-10x^3+25x^2-20x+4=0\)

d) \(2x^4+12x^3+7x^2-33x+5=0\)

e) \(\left(x^2-3x+3\right)^2-3x^2+8x-6=0\)

f) \(\left(x-3\right)\left(x-1\right)\left(x+2\right)\left(x+6\right)-40x^2=0\)