若(x+3)(x+n)=x2+mx-15,则m的值为_.

问题描述:

若(x+3)(x+n)=x2+mx-15,则m的值为______.

∵(x+3)(x+n)=x2+(3+n)x+3n,
∴x2+(3+n)x+3n=x2+mx-15,

3+n=m
3n=−15

∴m=-2,n=-5.
故本题答案为:-2.