\(\left(5x-1\right)^2+2\left(1-5x\right)\left(4+5x\right)+\left(5x+4\right)^2\)

\(=\left(5x-1\right)^2-2\left(5x-1\right)\left(5x+4\right)+\left(5x+4\right)^2\)

\(=\left[\left(5x-1\right)-\left(5x+4\right)\right]^2\)

\(=\left(5x-1-5x-4\right)^2\)

\(=\left(-5\right)^2\)

\(=25\)

  A = (5\(x\) + 1)² + (5\(x\) - 1)² - 2.( 5\(x\) +1).(5\(x\) - 1) tại \(x\) = 1

Thay \(x\) = 1 vào A ta có:

A = (5.1 + 1)² + (5.1 - 1)² - 2.(5.1 + 1).(5.1 - 1)

A = 6² + 4² - 2.6.4 

A = 36 + 16 - 48

A = 52 - 48

A = 4

A

A

\(2^3-\left(5x\right)^3-5\times\left(5x\right)^2\)+ 5

\(=8-125x^3-125x^2+5\)

\(=-125x^2\left(x-1\right)+13\)

Ngọc Vĩ : bạn giải ko sai .. -_- đấy là giống cách mình thôi 

Hoàng Anh Tú : nhầm dấu r kìa bạn ê -_-

Ngọc Nguyễn Minh ; bài này nè :)) làm đi

\(a,P\left(x\right)+Q\left(x\right)=2x^2+5x-1+2x^2-5x-7=4x^2-8\)

\(b,P\left(x\right)-Q\left(x\right)=\left(2x^2+5x-1\right)-\left(2x^2-5x-7\right)=2x^2+5x-1-2x^2+5x+7=10x+6\)

a) P(x) + Q(x)

= (2x² + 5x - 1) + (2x² - 5x - 7)

= 2x² + 5x - 1 + 2x² - 5x - 7

= (2x² + 2x²) + (5x - 5x) + (-1 - 7)

= 4x² - 8

b) P(x) - Q(x)

= (2x² + 5x - 1) - (2x² - 5x - 7)

= 2x² + 5x - 1 - 2x² + 5x + 7

= (2x² - 2x²) + (5x + 5x) + (-1 + 7)

= 10x + 6

`N-(6xy^2-5x)=(7+xy^2+5x)`

`-> N = ( 7 + xy^2 + 5x )+( 6xy^2 - 5x )`

`-> N = 7 + xy^2 + 5x +6xy^2 - 5x`

`-> N = ( 5x - 5x ) + ( 6xy^2 + xy^2 ) + 7`

`-> N = 7xy^2 + 7`