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令t=x²+3xt²+2t-1680=0解得t=40或t=-42x²+3x=40或x²+3x=-42x²+3...