Đáp án:

Bài `9:`

`a) A = 7/9 x^3y^2 . (6/11 axy^3) + (-5bx^2y^4) . (-1/2 a xz) + ax(x^2y)^3`

      ` = (7/9 . 6/11) . a . (x^3 . x) . (y^2 . y^3) + (-5 . (-1)/2) . ab . (x^2 . x)y^4 z + ax . x^6 . y^3`

      ` = 14/33 ax^4y^5 + 5/2 ab . x^3y^4z + ax^7y^3`

`b) B = ( (3x^4y^4)^2 . (1/16 x^3y) . (8x^(n-7)) . (-2x^(7-n)))/(15x^3y^2 . (0,4 ax^2y^2z^2)^2)`

ĐK : `axyz \ne 0`

       ` = (9x^8y^8 . (1/16x^3y) . (8x^(n-7)) . (-2x^(7-n)) )/(15x^3y^2 . 0,16 . a^2x^4y^4z^4)`

       ` = ( (9 . 1/16 . 8 . (-2)) . (x^8 . x^3 . x^(n-7) . x^(7-n)) . (y^8 . y))/( (15.0,16) . a^2 . (x^3 . x^4) . (y^2 . y^4) . z^4)`

        ` = ( -9 . x^11 . y^9)/(2,4 . a^2 . x^7 . y^6 . z^4)`

        ` = (-15x^4y^3)/(4a^2z^4)`