四道因式分解题目,帮忙解决①x^2+7x-18；②x^2-2x-15；③y^2-8y+15；④m^2-2m-3.

1.(x-2)(x+9)
2.(x+3)(x-5)
3.(y-3)(y-5)
4.(m+1)(m-3)

(x-2)(x+9)
(x-5)(x+3)
(y-3)(y-5)
(m-3)(m+1)

解
x²+7x-18
1 9
1 -2
=(x+9)(x-2)
x²-2x-15
1 -5
1 3
=(x-5)(x+3)
y²-8y+15
1 -5
1 -3
=(y-5)(y-3)
m²-2m-3
1 -3
1 1
=(m-3)(m+1)