a) `A= 7/2 x^4y^3 -5x^2y^5 -6y + 8x^2y^5 - 1/3 x^4y^3 -1/2y`
`A= (7/2 x^4y^3 -1/3 x^4y^3) - (5x^2y^5 - 8x^2y^5) - (6y+ 1/2 y)`
`A= 19/6 x^4y^3 + 3x^2y^5 - 13/2 y`
b) Thay `x= -2; y= 3/4` vào `A` ta được:
`A= 19/6 . (-2)^4 . (3/4)^3 + 3.(-2)^2 . (3/4)^5 - 13/2 . 3/4`
`A= 19/6 . 16 . 27/64 + 3.4 . 243/1024 - 39/8`
`A= 171/8 + 729/256 - 39/8`
`A= 4953/256`
Vậy `A= 4953/256` khi `x= -2; y= 3/4`