Each term in the first bracket has to be multiplied by each term in the second bracket.
(color(red)(x^2) +color(blue)(3x)+color(green)(10))(4x^2-2x-7)(x2+3x+10)(4x2−2x−7)
=color(red)(x^2)(4x^2-2x-7) +color(blue)(3x)(4x^2-2x-7)+color(green)(10)(4x^2-2x-7)=x2(4x2−2x−7)+3x(4x2−2x−7)+10(4x2−2x−7)
=color(red)(4x^4-2x^3-7x^2) +color(blue)(12x^3-6x^2-21x)+color(green)(40x^2-20x-70)=4x4−2x3−7x2+12x3−6x2−21x+40x2−20x−70
Now simplify by collecting the like terms,
=(4x^4)+(-2x^3+12x^3)+(-7x^2-6x^2+40x^2)+(-21x-20x)+(-70)=(4x4)+(−2x3+12x3)+(−7x2−6x2+40x2)+(−21x−20x)+(−70)
=4x^4+10x^3+27x^2-41x-70=4x4+10x3+27x2−41x−70