a) [TEX]9x^2+90x+225-(x-7)^2[/TEX]
[TEX]=(3x+15)^2-(x-7)^2[/TEX]
[TEX]=[3x+15-(x-7)](3x+15+x-7)[/TEX]
[TEX]=(3x+15-x+7)(4x+8)[/TEX]
[TEX]=(2x+22).4(x+2)[/TEX]
[TEX]=2(x+11).4(x+2)[/TEX]
[TEX]=2.4(x+11)(x+2)[/TEX]
[TEX]=8(x+11)(x+2)[/TEX]
b) bỏ qua :v
c) [TEX]x^2(x-2)^2-(x-2)^2-x^2+1[/TEX]
[TEX]=[x(x-2)]^2-(x^2-4x+4)-x^2+1[/TEX]
[TEX]=(x^2-2x)^2-x^2+4x-4-x^2+1[/TEX]
[TEX]=x^4-4x^3+4x^2-x^2+4x-4-x^2+1[/TEX]
[TEX]=x^4-4x^3+2x^2+4x-3[/TEX]
đến đây có thể làm tiếp