` color{#e6f0ff}{@}color{#c7ddff}{T}color{#99c2ff}{o}color{#66a3ff}{r}color{#3385ff}{a}color{#0066ff}{U}color{#0044cc}{F}color{#002d80}{O}color{#001b4d}{@} `

Bài ` 2 : `

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

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

` = [ ( 5x + 1 ) - ( 5x - 1 ) ]^2 `

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

` = 2^2 `

` = 4 `

` c) 3x ( x + 2 ) - 5x ( 1 - x ) - 8 ( x^2 - 2 ) `

` = 3x^2 + 6x - 5x + 5x^2 - 8x^2 + 16 `

` = x + 16 `

` e) ( 7x - 3 ) ( 2x + 1 ) - ( 5x - 3 ) ( x + 4 ) - 9x^2 + 18x `

` = 14x^2 + 7x - 6x - 3 - 5x^2 - 20x + 3x + 12 - 9x^2 + 18x `

` = 14x^2 + x - 3 - 5x^2 - 17x + 12 - 9x^2 + 18x `

` = ( 14x^2 - 5x^2 - 9x^2 ) + ( x - 17x + 18x ) - ( 3 - 12 ) `

` = 2x + 9 `