因式分解(1)9a的平方-b的平方+2b-1 (2)x^3+3x^2-4x-12 (3)1/4a^3+1/3a^2b+1

(1)9a的平方-b的平方+2b-1
=(3a)²-(b-1)²
=(3a+b-1)(3a-b+1)
(2)x^3+3x^2-4x-12
=x²(x+3)-4(x+3)
=(x²-4)(x+3)
=(x+2)(x-2)(x+3)
(3)1/4a^3+1/3a^2b+1/9ab²
=a[(1/2a)²+2×(1/2a)×(1/3b)+(1/3b)²]
=a(1/2a+1/3b)²