若x方+mx-15=(x+3)x(x+n)则m=_____

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若x方+mx-15=(x+3)x(x+n)则m=_____

若x方+mx-15=(x+3)x(x+n)则m=_____
若x方+mx-15=(x+3)x(x+n)则m=_____

若x方+mx-15=(x+3)x(x+n)则m=_____
结论:m=-2;
因为3n=-15,n=-5.
由-5x+3x=mx
-2x=mx,
故m=-2

∵(x+3)(x+n)=x2+(3+n)x+3n,
∴x2+mx-15=x2+(3+n)x+3n,
∴m=3+n,3n=-15,
解得m=-2,n=-5.

(x+3)(x+n)=x方+(3+n)x+3n=x方+mx-15
对比系数相等得:
3+n=m
3n=-15
解得:n=-5
m=-2