(1)x^2-7x-18 (2)a^2+12ab+32b^2 (3)a^4-3a

(1)x^2-7x-18=(x+2)(x-9)
(2)a^2+12ab+32b^2=(a+4b)(a+8b)
(3)a^4-3a^2-4=（a²-4)(a²+1)=(a-2)(a+2)(a²+1)
(4)x^4-13x^2+36=(a²-4)(a²-9)=(a-2)(a+2)(a-3)(a+3)
(5)(a+2b)^2-15(a+2b)-16=(a+2b+1)(a+2b-16)
(6)a^2b^2-23abc+60c^2=(ab-3c)(ab-20c)
(7)a^3-5a^2b-24ab^2=a(a²-5ab-24b²)=a(a+3b)(a-8b)
(8)3ab^2-9a^2b^2+6a^3b^2=3ab²(1-3a+2a²)=3ab²(1-2a)(1-a)