Khai triển hằng đẳng thức:
1) x³-9=
2) 8x³-64=
3) 8x³+64=
4) 216x³-1=
5) 216x³+1=
5) x³+1=
6) x³-1=
7) (x²+2)³-1=
8) (x²-2)³-8=
Khai triển hằng đẳng thức: 1) x³-9= 2) 8x³-64= 3) 8x³+64= 4) 216x³-1= 5) 216x³+1= 5) x³+1= 6) x³-1= 7) (x²+2)³-1= 8) (x²-2)³-8=
By Alaia
$1) x^3-8=(x-2)(x^2+2x+4)$ $\text{(mình sửa lại đề nha). }$
$2) 8x^3-64=(2x)^3-4^3=(2x-4)(4x^2+8x+16)$
$3) 8x^3+64=(2x)^3+4^3=(2x+4)(4x^2-8x+16)$
$4) 216x^3-1=(6x)^3-1^3=(6x-1)(36x^2+6x+1)$
$5) 216x^3+1=(6x)^3+1^3=(6x+1)(36x^2-6x+1)$
$6)x^3+1=(x+1)(x^2-x+1)$
$7)x^3-1=(x-1)(x^2+x+1)$
$8)(x^2+2)^3-1=(x^2+2-1)[(x^2+2)^2+x^2+2+1]=(x^2+1)(x^4+4x^2+4+x^2+2+1)=(x^2+1)(x^4+5x^2+7)$
$9)(x^2-2)^3-8=(x^2-2)^3-2^3=(x^2-2-2)[(x^2-2)+(x^2-2).2+4]= (x^2-4)[x^4-4x^2+4+2x^2-4+4]=(x-2)(x+2)(x^4-2x^2+4)$
$\text{Bài này áp dụng HĐT số 6, 7 cụ thể: }$
$A^3+B^3=(A+B)(A^2-AB+B^2)$
$A^3-B^3=(A-B)(A^2+AB+B^2).$
Đáp án:
Giải thích các bước giải:
1. x³ – 8
= x³ – 2³
= ( x – 2)( x² + 2x + 4)
2. 8x³ – 64
= ( 2x )³ – 4³
= ( 2x – 4)(4x² + 8x + 16)
3. 8x³ + 64
= ( 2x )³ + 4³
= ( 2x + 4 )( 4x² – 8x + 16)
4. 216x³ – 1
= ( 6x)³ – 1³
= ( 6x – 1 )( 36x² + 6x + 1 )
5. 216x³ + 1
= ( 6x )³ + 1³
= ( 6x + 1 )( 36x² – 6x +1)
6. x³ + 1
= x³ + 1³
= ( x +1)( x² – x +1)
7. x³ – 1
= ( x -1)( x² + x +1)
8. ( x² + 2 )³ -1
= ( x² + 2 )³ -1³
=( x² + 2 -1)[( x² +2)² + 1(x² +2)+1]
= ( x² +1)(x⁴ + 4x² + 4+ x² +2 +1)
= ( x² +1)( x⁴ + 5x² + 7)
9. (x² – 2)³ – 8
= ( x² – 2 )³ – 2³
= ( x² – 2 – 2 )[ ( x² -2)²+ 2(x² -2)+ 4]
= (x² – 4)( x⁴ – 4x² + 4 +2x² -4 + 4)
= (x – 2)(x + 2)( x⁴ -2x + 4)