若(x+5)(x-3)是二次三项式x2-kx-15的因式,那么k的值是(  ) A.8 B.-8 C.2 D.-2

问题描述:

若(x+5)(x-3)是二次三项式x2-kx-15的因式,那么k的值是(  )
A. 8
B. -8
C. 2
D. -2

(x+5)(x-3)=x2-3x+5x-15=x2+2x-15=x2-kx-15,
则k=-2.
故选D.