x(x+1)(x+2)(x+3)=1680[x(x+3)][(x+1)(x+2)]=1680(x²+3x)(x²+3x+2)=1680(x²+3x)²+2(x²+3x)-1680=0(x²+3x+42)(x²+3x-40)=0(x²+3x+42)(x+8)(x-5)=0(x²+3x+42>0)(x+8)(x-...