Question

若x^2+4x-4=0,则3x^2+12x-5的值为_____.分解因式9a-a^3=_____.

Answer 1

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)