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______.
答
∵(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.