a.

\(x^2+xy+x=x\left(x+y+1\right)\)

Tại \(x=77;y=22\Rightarrow x\left(x+y+1\right)=77\left(77+22+1\right)=77.100=7700\)

b.

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

\(=\left(53-3\right)^2=50^2=2500\)

c.

\(x\left(x-1\right)-y\left(1-x\right)=x\left(x-1\right)+y\left(x-1\right)=\left(x+y\right)\left(x-1\right)\)

\(=\left(2001+1999\right)\left(2001-1\right)=4000.2000=8000000\)

1/

a)5x – 20y=5(x-4y)

b) 5x.(x –  1) –  3x(x – 1)=2x(x-1)

c) x.(x+y) – 5x – 5y=c) x.(x+y) – 5(x+y)=(x-5)(x+y)

2/

a)x² + xy + x = x(x+y+1)=77.(77+22+1)=77.100=7700

b)  x . ( x – y ) + y . ( y – x )=(x-y)(x-y)=(x-y)²=(53-3)²=2500

3/

a) X + 5x² = 0

⇒x(x+5)=0

⇒hoặc x=0

x+5=0⇒x=-5

b)x + 1 = ( x + 1 )² 

⇒(x + 1)-( x + 1 )² =0

⇒x(x+1)=0

⇒ hoặc x=0

hoặc x+1=0⇒x=-1

4/

a) 97 . 13 + 130 . 0,3 = 97.13+13.10.0,3=97.13+13.3=100.13=1300

b)86 . 153 – 530 . 8,6=86.153–53.10.8,6=86.153-53.86=86.100=8600

C) 85 .12,7 + 5,3 . 12,7= 12,7(85+5,3)=12,7.90,3=1146,81

D)52.143 – 52 . 39 – 8.26=52(143-39)-8,26=52.104-8,26=5399,74

Bài 1:  

a) 5x-20y=5(x-4y)

b) \(5x\left(x-1\right)-3x\left(x-1\right)=2x\left(x-1\right)\)

c) \(x\left(x+y\right)-5x-5y=\left(x+y\right)\left(x-5\right)\)

Bài 2: 

a) \(x^2+xy+x\)

\(=x\left(x+y+1\right)\)

\(=77\cdot\left(77+22+1\right)\)

=7700

b) \(x\left(x-y\right)+y\left(y-x\right)\)

\(=x\left(x-y\right)-y\left(x-y\right)\)

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

\(=50^2=2500\)

a.\(x^2+xy+x=x\left(x+y+1\right)=77\left(77+22+1\right)=77.100=7700\)

b.\(x\left(x-y\right)+y\left(y-x\right)=\left(x-y\right)^2=\left(53-3\right)^2=50^2=2500\)

Đặt A = x² + xy + x 

= x(x + y + 1) 

Thay x = 77 ; y = 22 vào biểu thức ta được 

A = 77(77 + 22 + 1) = 77.100 = 7700

b) Đặt B =  x(x - y) + y(y - x) 

= (x - y)² 

Thay x = 53 ; y = 3 vào biểu thức ta được 

B = (53  - 3)² = 50² = 2500

có ai biết câu này ko:  85.12,7 + 5.3.12,7           

Ta có:  x 2  + xy + x = x(x + y + 1)

Thay x = 77, y = 22 vào biểu thức, ta được:

x(x + y + 1) = 77.(77 + 22 + 1) = 77.100 = 7700

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

\(=x^3-x^2y-x^2y+xy^2-x^3-2xy^2\)

\(=-2x^2y-xy^2\)

\(=-2\cdot2^2\cdot\left(-3\right)-2\cdot\left(-3\right)^2\)

\(=8\cdot3-2\cdot9\)

=6

a) \(P=x\left(x-y\right)+y\left(x-y\right)=\left(x-y\right)\left(x+y\right)=x^2-y^2=5^2-4^2=9\)

b) \(Q=x\left(x^2-y\right)-x^2\left(x+y\right)+y\left(x^2-x\right)=x^3-xy-x^3-x^2y+x^2y-xy=0\)

a: \(=\left(x-y\right)\left(x+y\right)\)

\(=74\cdot100=7400\)

c: \(=\left(x+2\right)^3\)

\(=10^3=1000\)

a) \(=\left(x-y\right)\left(x+y\right)\)

    Thay \(x=87;y=13\) ta đc:   \(\left(87-13\right)\left(87+13\right)=74\cdot100=7400\)

b)\(=\left(x-y\right)\left(x^2+xy+y^2\right)=x^3-y^3\)

   Thay \(x=10;y=-1\) ta đc:

    \(10^3-\left(-1\right)^3=1000-1=999\)

c)\(=\left(x+2\right)^3\)

   Thay \(x=8\) ta đc: \(\left(8+2\right)^3=10^3=1000\)

d)\(=x^2-8x+16+1=\left(x-4\right)^2+1\)

   Thay \(x=104\) ta đc: \(\left(104-4\right)^2+1=100^2+1=10001\)