Đáp án:
`b. (x^2- 8)^2 + 36`
`= x^4 - 16x^2 + 64 + 36`
`= x^4 - 16x^2 + 100`
`= x^4 - 36x^2 + 20x^2 + 100`
`= (x^4 + 20x^2 + 100) - 36x^2`
`= (x^2 + 10)^2 - (6x)^2`
`= (x^2 + 10 - 6x)(x^2 + 10+6x)`
`c, 81x^4 + 4`
`= 81x^4 + 54x^3 - 54x^3 + 18x^2 - 18x^2 + 12x - 12x + 12x + 4`
`= (81x^4 + 54x^3 + 18x^2 )- (54x^3 + 36x^2 + 12x) + (18x^2 + 12x + 4)`
`= 9x^2 ( 9x^2 + 6x^3 + 2) - 6x(9x^2 + 6x^3 + 2) + 2(9x^2 + 6x + 2)`
`= (9x^2 - 6x + 2)( 9x^2 + 6x + 2)`
`d, x^5 + x + 1`
`= x^5 -x^2 + x^2 + x + 1`
`=x^2 ( x^3 - 1) + (x^2 + x+1)`
`= x^2 ( x-1)(x^2 + x +1) + (x^2 + x+1)`
`=( x^3 - x^2 )( x^2 + x +1) + (x^2 + x +1)`
`=(x^2 + x + 1)(x^3 - x^2 + 1)`
