(x-4)(x+1)(x+2)(x+7)+56=0(x-4)(x+7)(x+1)(x+2)+56=0(x²+3x-28)(x²+3x+2)+56=0(x²+3x-28)²+30(x²+3x-28)+56=0(x²+3x)(x²+3x-26)=0x(x+3)(x²+3x-26)=0