x²-x-2=0 ;
(x-2)(x+1)=0
x=2或x=-1
x²-2x-3=0 ;
(x-3)(x+1)=0
x=3或x=-1
(x+1)²=(x+1)+56
(x+1)²-(x+1)-56=0
(x+1-8)(x+1+7)=0
(x-7)(x+8)=0
x=7或x=-8