Bài 1: Thu gọn biểu thức a) 6( 2x – 1 ) ² + 5( x – 2 )( x + 3 ) – 2( 5 – 2x ) ² b) ( 9x – 1 ) ² + ( 1 – 5x ) ² + 2( 9x – 1 )( 1 – 5x ) c) ( x ² – 5x

`a) 6(2x-1)^2 + 5(x-2)(x+3) – 2(5-2x)^2`

`= 6(4x^2 – 4x + 1) + 5(x-2)(x+3) – 2(5-2x)^2`

`= 6(4x^2-4x+1) + 5(x-2)(x+3) – 2(25-20x+4x^2)`

`= 24x^2 – 24x + 6 + 5x^2 + 5x – 30 – 2(25-20x+4x^2)`

`= 24x^2 – 24x + 6 + 5x^2 – 30 – 50 + 40x – 8x^2`

`= 21x^2 + 21x – 74`

`b) (9x-1)^2 + (1-5x)^2 + 2(9x-1)(1-5x)`

`= 81x^2 – 18x + 1 + (1-5x)^2 + 2(9x-1)(1-5x)`

`= 81x^2 – 18x + 1 + 1 – 10x + 25x^2 +2(9x-1)(1-5x)`

`= 81x^2 – 18x + 1 + 1 – 10x + 25x^2 – 90x^2 + 28x – 2`

`= 16x^2`

`c) (x^2-5x+1)^2 + 2(5x-1)(x^2-5x+1)+(5x-1)^2`

`= (x^2-5x+1)(x^2-5x+1) + 2(5x-1)(x^2-5x+1) + 25x^2 – 10x + 1`

`= x^4 – 10x^3 + 27x^2 – 10x + 1 + 2(5x-1)(x^2-5x+1)+25x^2 – 10x + 1`

`= x^4 – 10x^3 + 27x^2 – 10x + 1 + 10x^3 – 52x^2 + 20x – 2 + 25x^2 – 10x + 1`

`= x^4`