【在线=】请教一些因式分解

1用十字相乘法
a^2-5a+4=(a-1)(a-4)

2先化简再用用十字相乘法
(x+2)(x+3)+3x+1
=X^2+8X+7
=(X+7)(X+1)

3直接做
x^2-4y^2+x+2y
=(x+2y)*(x-2y)+x+2y
=(x+2y)*(x-2y+1)

1.(a-1)*(a-4)
2.原式＝x^2+5x+6+3x+1=x^2+8x+7=(a+1)*(a+7)
3.原式＝(x+2y)*(x-2y)+x+2y=(x+2y)*(x-2y+1)

1 =(a-1)(a-4)
2 =x^2+8x+7=(x+7)(x+1)
3 =(x-2y)(x+2y)+(x+2y)=(x+2y)(x-2y+1)

(a-1)(a-4)
(x+1)(x+7)
(x+2y)(x-2y+1)