Đáp án:
7. `a^6 - b^3`
`= (a^2)^3 - b^3`
`= (a^2 -b) [( a^2)^2+ a^2b + b^2]`
`= ( a^2 -b) ( a^4 + a^2b +b^2)`
8. ` x^3 + 8y^3`
`= x^3 + (2y)^3`
`= (x + 2y) [ x^2 - 2y.x + (2y)^2]`
`= ( x + 2y) [ x^2 - 2y.x + (2y)^2]`
`= ( x+ 2y) (x^2 - 2xy + 4y^2)`
ct :
`A^3 - B^3 = (A - B) (A^2 + AB + B^2)`
`A^3 + B^3 = ( A + B) (A^2 - AB + B^2)`
mong ctlhn ạ~~