十字相乘法(1)x2-x-6(2)x2-x-1(3)x2-2xy-5y2(4)6y2-y-1(5)6y2-5y-1

Question

十字相乘法
(1)x2-x-6 (2)x2-x-1 (3)x2-2xy-5y2
(4)6y2-y-1 (5)6y2-5y-1

Answer 1

(1)x2-x-6
=(x-3)(x+2)
2)x2-x-1
=x^2-x+1/4-5/4
=(x-1/2)^2-5/4
=(x-1/2+根号5/2）（x-1/2-根号5/2)
(3)x2-2xy-5y2
=x^2-2xy+y^2-6y^2
=(x-y)^2-6y^2
=(x-y+根号6y)(x-y-根号6y)