a) $(3x+5)^2\\=(3x)^2+2.3x.5+5^2\\=9x^2+30x+25$

b) $(6x+\dfrac{1}{3})^2\\=(6x)^2+2.6x.\dfrac{1}{3}+(\dfrac{1}{3})^2\\=36x^2+4x+\dfrac{1}{9}$

c) $(5x-4y)^2\\=(5x)^2-2.5x.4y+(4y)^2\\=25x^2-40xy+16y^2$

d) $(5x-3)(5x+3)\\=(5x)^2-(3)^2\\=25x^2-9$

\(A=\left(x^2-4y^2\right)\left(x^2-2xy+4y^2\right)\left(x^2+2xy+4y^2\right)\)

\(A=\left(x-2y\right)\left(x+2y\right)\left(x^2-2xy+4y^2\right)\left(x^2+2xy+4y^2\right)\)

\(A=\left(x-2y\right)\left(x^2+2xy+4y^2\right)\left(x+2y\right)\left(x^2-2xy+4y^2\right)\)

\(A=\left[x^3-\left(2y\right)^3\right]\left[x^3+\left(2y\right)^3\right]\)

\(A=\left[x^3-8y^3\right]\left[x^3+8y^3\right]\)

\(A=x^6-64y^6\)

5:

a: (2x-5)(2x+5)=4x^2-25

b: (3x-5y)(3x+5y)=9x^2-25y^2

c: (3x+7y)(3x-7y)=9x^2-49y^2

d: (2x-1)(2x+1)=4x^2-1

4:

a: 2003*2005=(2004-1)(2004+1)=2004^2-1<2004^2

b: 8(7^2+1)(7^4+1)(7^8+1)

=1/6*(7-1)(7+1)(7^2+1)(7^4+1)(7^8+1)

=1/6(7^2-1)(7^2+1)(7^4+1)(7^8+1)

=1/6(7^16-1)<7^16-1

5:

a: (2x-5)(2x+5)=4x^2-25

b: (3x-5y)(3x+5y)=9x^2-25y^2

c: (3x+7y)(3x-7y)=9x^2-49y^2

d: (2x-1)(2x+1)=4x^2-1

mik chỉ biết bài 5 thôi !

\(x^3-64=x^3-4^3=\left(x-4\right)\left(x^2+4x+16\right)\)

\(x^3-64x\)

\(=x\left(x^2-64\right)=x\left(x^2-8^2\right)\)

\(=x\left(x-8\right)\left(x+8\right)\)

Chọn B

B

B

a: \(=x^2-12x+36\)

b: \(=x^3+9x^2+27x+27\)

A.x=6

b.x=-3