①x²- 2 =(x＋√2)(x-√2)②5x²-3=(√5x＋√3)(√5x-√3)③（x-2）²-x+2=（x-2）（x-2-1）=(x-2)(x-3)④y4-3y3-28y²=y²(y²-3y-28)=y²(y+4)(y-7)