题目如下，求因式分解。

1.x²+10x+21=(x+3)(x+7)2.x²+6x+5=(x+1)(x+5)3.x²+6x-16=(x+8)(x-2)4.x²-17x+16=(x-1)(x-16)5.x²-x-12=(x-4)(x+3)6.x²+2x-15=(x+5)(x-3)7.x²-5x-6=(x-6)(x+1)8.x²+11x+24(x+3)(x+8)9.x²+10x+21=(x+3)(x+7)10.x²+4x-12=(x+6)(x-2)11.x²+4x+4=(x+2)²12.x²+10x+25=(x+5)²13.x²-8x+16=(x-4)²14.二次三项式x²+mx-15可因式分解为（x-5）（x+n）,则m=-2 n=3.

1. x²+10x+21=(x+7)(x+3) 2. x²+6x+5=(x+5)(x+1)3. x²+6x-16=(x+8)(x-2)4.x²-17x+16=(x-16)(x-1)5.x²-x-12=(x-4)(x+3)6. x²+2x-15=(x+5)(x-3)7.x²-5x-6=(x-6)(x+1)8.x²+11x+24=(x+8)(x+3)9.x²+10x+21=(x+7)(x+3)10.x²+4x-12=(x+6)(x-2)11.x²+4x+4=(x+2)²12.x²+10x+25=(x+5)²13.x²-8x+16=(x-4)²14.x²+mx-15=(x-5)(x+n)x²+mx-15=x²+nx-5x-5nx²+mx-15=x²+(n-5)x-5n5n=15 n=3；m=n-5 m=3-5 m=-2结果：m=-2 n=3。