(1)(a+b)(a+b-6)+9 (2)x^2-9y^2+x+3y

问题描述:

(1)(a+b)(a+b-6)+9 (2)x^2-9y^2+x+3y

(a+b)(a+b-6)+9
=(a+b)^2-6(a+b)+9
=(a+b-3)^2
x^2-9y^2+x+3y
=(x-3y)(x+3y)+(x+3y)
=(x+3y)(x-3y+1)