\(4x^2-25y^2\)

\(\left(2x\right)^2-\left(5y\right)^2\)

\(\left(2x-5y\right)\left(2x+5y\right)\)

chọn c

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

n) \(\dfrac{4}{49}-4x^2=\left(\dfrac{2}{7}-2x\right)\left(\dfrac{2}{7}+2x\right)\)

o) \(\left(x-3\right)\left(x+3\right)=x^2-9\)

Mik cần gấp 

Chọn B

B

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

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

\(36-12x+x^2=\left(6-x\right)^2\)

\(\left(x+5y\right)^2=x^2+10xy+25y^2\)

\(4x^2-12x+9=\left(2x-3\right)^2\)

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

\(b,\left(5x-7y^2\right).\left(5x+7y^2\right)=\left(25x^2-49y^4\right)\)

a) (2x-y)² = (2x)² - 2.2x.y + y² =4x²-4xy+y²

b)(5x-7y²).(5x+7y²) = (5x)² - (7y²) ² =25x² - 49y⁴ 

         câu c,d mk ko bít làm

câu a/hằng đẳng thức (A+B)² trong đó A là 2x; B là y

câu b/ thu gọn thanh hằng đẳng thức A² -B² trong đó A là 5x B là 7y

tương tự cũng vậy

a) \(=x^3+27-54-x^3=-27\)

b) \(=8x^3+y^3\)

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 !

\(a,\left(6x+5y\right)\left(6x-5y\right)\)

\(=\left(6x\right)^2-\left(5y\right)^2\)

\(=36x^2-25x^2\)

\(b,\left(-4xy-5\right)\left(5-4xy\right)\)

\(=-\left(5+4xy\right)\left(5-4xy\right)\)

\(=-[5^2-\left(4xy\right)^2]\)

\(=-\left(25-16xy^2\right)\)

\(c,\left(3x-4\right)^2+2.\left(3x-4\right).\left(4-x\right)+\left(4-x\right)^2\)

\(=\left(3x-4\right)\left(3x-4+2\right)\left(4-x\right)\left(1+4-x\right)\)

\(=\left(3x-4\right)\left(3x-2\right)\left(4-x\right)\left(5-x\right)\)

a/ \(\left(x-2\right)\left(2+x\right)=\left(x-2\right)\left(x+2\right)=x^2-4\)

b/ \(\left(1-3x\right)\left(3x+1\right)=\left(1-3x\right)\left(1+3x\right)=1-\left(3x\right)^2=1-9x^2\)

c/ \(\left(4x+5y\right)\left(5y-4x\right)=\left(5y+4x\right)\left(5y-4x\right)=\left(5y\right)^2-\left(4x\right)^2=25y^2-16x^2\)