若x^2+4x-4=0,则3x^2+12x-5的值为_____.分解因式9a-a^3=_____.
问题描述：
若x^2+4x-4=0,则3x^2+12x-5的值为_____.分解因式9a-a^3=_____.
答
x^2+4x-4=0,
x^2+4x=4
3x^2+12x-5
=3(x^2+4x)-5
=3*4-5
=12-5
=7
9a-a^3
=a(9-a^2)
=a(3-a)(3+a)