(4)6y²-11y-10
=(2y-5)(3y+2)
(5)解方程x²-2x=3
x²-2x-3=0
(x-3)(x+1)=0
x=3或x=-1
(6)(x+y)²+4(x+y)+3
=(x+y+3)(x+y+1)
(7)(m+n)²-3(m+n)+2
=(m+n-2)(m+n-1)
(8)x²-7x+6
=(x-6)(x-1)
(9)3x²+2x-1
=(3x+1)(x-1)
(10)x²+5x-6
=(x+6)(x-1)
(11)4x²-5x-9
=(4x-9)(x+1)
(12)15x²-23x+8
=(15x-8)(x-1)