Đáp án:
Giải thích các bước giải:
`a ) x^ 3 - x^ 2 - 4`
`= x^ 3 + x ^2- 2 x ^2 + 2 x - 2 x - 4`
`=( x^ 3 + x ^2 + 2 x) - (2 x ^2 + 2 x+ 4)`
`= x ( x^ 2 + x + 2 ) - 2 ( x ^2 + x + 2 )`
`= ( x - 2 ) ( x ^2 + x + 2 )`
`b ) 4x^4 + 81`
`= 4x^4 + 81 + 36x^2 - 36x^2`
`=( 4x^4 + 36x^2 + 81)- 36x^2`
`= [(2x^2)^2 + 2.2x^2. 9+ 9^2] - 36x^2`
`= (2x^2 + 9)^2 - (6x)^2`
`= (2x^2 + 9 - 6x)(2x^2 + 9 + 6x)`
`c ) 64x^4 + y^4`
`= 64x^4 +16x^2y^2+ y^4 - 16x^2y^2`
`= (8x^2)^2 +2. 8x^2. y^2+ (y^2)^2 - 16x^2y^2`
`= (8x^2+y^2)^2 - (4xy)^2`
`= (8x^2+y^2- 4xy) (8x^2+y^2 + 4xy)`
`d ) x^5+x-1`
`= x^5-x^4+x^4+x^3-x^3+x^2-x^2+x-1`
`= (x^5-x^4+x^3)+(x^4-x^3+x^2)-(x^2-x+1)`
`= x^3(x^2-x+1)+x^2(x^2-x+1)-(x^2-x+1)`
`= (x^2-x+1)(x^3+x^2-1)`
