Bài 2: 

a: \(A=\left(x+1\right)^3+5=20^3+5=8005\)

b: \(B=\left(x-1\right)^3+1=10^3+1=1001\)

h, \(27x^3-8=\left(3x-2\right)\left(9x^2+6x+4\right)\)

\(\Rightarrow\left(27x^3-8\right):\left(3x-2\right)\\ =\left(3x-2\right)\left(9x^2+6x+4\right):\left(3x-2\right)\\ =9x^2+6x+4\)

g, \(x^4-2x^2+1=\left(x^2-1\right)^2\)

\(\Rightarrow\left(x^4-2x^2+1\right):\left(1-x^2\right)\\ =\left(x^2-1\right)^2:\left(1-x^2\right)\\ =x^2-1\)

Câu 5:B

Câu 4: C

Câu 3: D

Câu 2: A

Câu 1: A

B)(5-3x)^2=25+9x^2-30x

c)(5-x^2)(5+x^2)=25-x^4

d)(5x-1)^3=125x^3-1+15x-75x^2

e)(x^2+3)(x^4+9-3x^2)=x^6+27

f)( x-4y)(x^2+4 xy+16 y^2)= x^3-64 y^3

a) \(=x^3+27-54-x^3=-27\)

b) \(=8x^3+y^3\)

a,\(\Leftrightarrow\left(x-1\right)^3+\left(2-x\right)\left(4+2x+x^2\right)+3x\left(x+2\right)-17=0\)

\(\Leftrightarrow x^3-3x^2+3x-1+8-x^3+3x^2+6x-17=0\)

\(\Leftrightarrow9x-10=0\)

\(\Leftrightarrow x=\frac{10}{9}\)

b,\(\Leftrightarrow x^3+8-x^3+2x-15=0\)

\(\Leftrightarrow2x=7\)

\(\Leftrightarrow x=\frac{7}{2}\)

c,\(\Leftrightarrow x^3-9x^2+27x-27-x^3+27+9x^2+18x+1-15=0\)

\(\Leftrightarrow45x=14\)

\(\Leftrightarrow x=\frac{14}{45}\)

d/x²-x-1/4

=-(x²+2.x.1/2+(1/2)²

=-(x+1/2)²

=(x-1/2)²

Đưa về hằng đẳng thức :

c) \(\)Câu này đề sai nhé:

Phải là: \(\left(x+3\right).\left(x^2-3x+9\right)\) hoặc \(\left(x-3\right).\left(x^2+3x+9\right)\) thì mới ra được hằng đẳng thức nhé.

d) \(x^2-x-\frac{1}{4}\)

\(=-\left(x^2+x+\frac{1}{4}\right)\)

\(=-\left[x^2+2.x.\frac{1}{2}+\left(\frac{1}{2}\right)^2\right]\)

\(=-\left(x+\frac{1}{2}\right)^2.\)

Chúc bạn học tốt!

a) (x+2)²-(x-2)(x+1)=3

<=>-(x-2)²-(x-2)(x+1)=3

<=>-(x-2)[(x-2)-(x+1)]=3

<=>(x+2).(-3)=3

=>x=-3