x^2+ax-9=(x+m)(x+n)m,n為正整數,則有自然數a的值?A.0,-8.8 B.正負8 C.0,-8 D.0,8

x^2+ax-9=(x+m)(x+n)m,n為正整數,則有自然數a的值?A.0,-8.8 B.正負8 C.0,-8 D.0,8


x^2+ax-9=(x+m)(x+n)=x^2+(m+n)x-mn

m+n=a
mn=-9=(-1)x9=1x(-9)=(-3)x3
故:a=m+n=8,-8,0