`a) A = (- 2x ^ 2 * y ^ 2 + 4xy - 6x * y ^ 3) :2xy= - x * y + 2 - 3y ^ 2`

Thay ` x = 1/2; y = 4`

` A = - 1/2 . 4 + 2 - 3.4 ^ 2=-2+2-3.16=-48`

`b,B = 25x ^ 3 - 10x * y ^ 2 + y ^ 4`

Thay ` x = 2, y=3 `

`B = 25.2 ^ 3 - 10.2 * 3 ^ 2 + 3 ^ 4= 25.8-20.9+81=101`

`C,C = (3x + 2) ^ 2 + 2(3x + 2)(2y - 1) + (2y - 1) ^ 2= (3x + 2 + 2y - 1) ^ 2= (3x + 2y + 1) ^ 2`

Thay `x = 1/3 ,y = 1/2`

` C=( 3 . 1/3 + 2 . 1/2 + 1 )^ 2= (1 + 1 + 1) ^ 3=27`

`@612009`