$6)x=7\implies 8=x+1\\
\implies P=x^{15}-8x^{14}+8x^{13}-8x^{12}+...-8x^2+8x-5
\\=x^{15}-x^{14}(x+1)+x^{13}(x+1)-x^{12}(x+1)+...-x^2(x+1)+x(x+1)-5
\\=x^{15}-x^{15}-x^{14}+x^{14}+x^{12}-x^{13}-x^{12}+...-x^3-x^2+x^2+x-5
\\=x-5=7-5=2$
$7)(a+b+c)(a^2+b^2+c^2-ab-bc-ca)
\\=(a+b+c)(a^2+2ab+b^2-ca-bc+c^2-3ab)
\\=(a+b+c)[(a+b)^2-(a+b)c+c^2]-3ab(a+b+c)
\\=(a+b)^3+c^3-3ab(a+b)-3abc
\\=a^3+b^3+c^3-3abc$
$8)\\a)(xy^2+x^2y+x^3+y^3)(x-y)
\\=(x-y)(x^3+x^2y+xy^2+y^3)
\\=x^4-y^4\\
b)(x^2+x+1)(x^2-x+1)
\\=(x^2+1)^2-x^2
\\=x^4+2x^2+1-x^2
\\=x^4+x^2+1\\
c)(5x-2x^2+3)(2x^2-3)
\\=[5x-(2x^2-3)](2x^2-3)
\\=5x(2x^2-3)-(2x^2-3)^2
\\=10x^3-15x-4x^4+12x^2-9$
$d)$ Câu này mk nghĩ là $8x$ thì hợp hơn ^^
$(4x^2-2x^3-8x+x^4+16)(x+2)
\\=(x+2)(x^4-x^3.2+x^2.2^2-x.2^2+2^4)
\\=x^5+2^5=x^5+32$
$1)\\a)3x(4x-3)-(2x-1)(6x+5)
\\=12x^2-9x-12x^2-4x+5
\\=-13x+5\\
b)2(3x-1)(2x+5)-(4x-1)(3x-2)
\\=12x^2+26x-10-12x^2+11x-2
\\=37x-12\\
c)(a-2)(a^2+a+1)-a(a^2-1)
\\=a^3+a^2+a-2a^2-2a-2-a^3+a
\\=-a^2-2$
[TẶNG BẠN] TRỌN BỘ Bí kíp học tốt 08 môn
