`a, (x-3)(x+3)(x+2)-(x-1)(x^2-3)-5x(x+4)^2-(x-5)^2`
`⇔ (x^2-9)(x+2)-(x^3-3x-x^2+3)-5x(x^2+8x+16)-(x^2-10x+25)`
`⇔ x^3+2x^2-9x-18-x^3+3x+x^2-3-5x^3-40x^2-80x-x^2+10x-25`
`⇔ -5x^3-38x^2-76x-46`
`b, (2x+3)^2+(x-1)(x+1)=5(x+2)^2-(x-5)(x-1)+(x+4)^2`
`⇔4x^2+12x+9+x^2-1=5(x^2+4x+4)-(x^2-x-5x+5)+x^2+8x+16`
`⇔5x^2+12x+8=5x^2+20x+20-x^2+x+5x-5+x^2+8x+16`
`⇔5x^2+12x+8-5x^2-20x-20+x^2-x-5x+5-x^2-8x-16=0`
`⇔ -22x-23=0`
`⇔-22x=23`
`⇔x=-23/22`
$\text{Vậy tập nghiệm của PT: S = {$\dfrac{-23}{22}$}}$