`e, (x+2y^2)^2=x^2+4xy^2+4y^4`.

`f, (2x+3y^2)^2=4x^2+6xy^2+9y^4.`

`c, (x^2-y^2)^2=(x^4-2x^2y^2+y^4`.

`d, (3x-y^2)^2=9x^2-6xy^2+y^4`.

`a, (x^2+9)^2=x^4+18x^2+81`.

`b, (2x^2+1)^2=4x^4+4x^2+1`

`k, (x-2y)^2=x^2-4xy+4y^2`.

`l, (2x-y)^2=4x^2-4xy+y^2`.

`i, (x+2y)^2=x^2+4xy+4y^2`.

`j, (x+5y)^2=x^2+10xy+25y^2`

`o, (2x-3y)^2=4x^2-12xy+9y^2`.

`p, (2x-5y)^2=4x^2-20xy+25y^2`.

`m, (3x+5y)^2=9x^2+30xy+25y^2`.

`n, (2x+3y)^2=4x^2+12xy+9y^2`

`= sqrt 9 - sqrt 16 + 13`.

`= 3-4+13`

`=12`.

Mình làm r nhé.

`(x+2).(y+3)=6`.

Do `x, y in NN`.

`=> (x+2) in Ư(6)`.

`<=> x+2 in {1,2,3,6}`

`@ x+2=1 <=> x=-1 => Ktm.`

`@ x+2=2 <=> x=0`.

     `y+3=3 <=> y=0`.

`@ x+2=3 <=> x=1`.

    `y+3=2 <=> y=-1(ktm)`.

`@x+2=6 <=> x=4.`

    `y+3=1 <=> y=-2(ktm)`.

Vậy `(x, y) = (0,0).`