-(a+1)^2+9(a-2)^2=9(a-2)^2-(a+1)^2=[3(a-2)+(a+1)][3(a-2)-(a+1)]=(4a-5)(2a-7)
:-(a+1)^2+9(a-2)^2=9﹙a-2﹚²-﹙a+1﹚²=[3﹙a-2﹚+﹙a+1﹚][3﹙a-2﹚-﹙a+1﹚]=﹙4a-5﹚﹙2a-7﹚
-(a+1)^2+9(a-2)^2=9(a-2)^2-(a+1)^2=【9(a-2)-(a+1)】【9(a-2)+(a+1)】=(8a-19)(10a-17)