6 (x-y) - 12 (x-y) ^2

(a^2-b^3) - 5 (b^3-a^2) - 3k (a^2-b^3)

6 (x-y) - 12 (x-y) ^2

6 (x-y) = 6x-6y

(x-y) ²=x²-2xy+y²

12 (x²-2xy+y²) = 12x²-24xy+12y²

6x-6y - (12x²-24xy+12y²) = 6x-6y-12x²+24xy-12y²

2) (a^2-b^3) - 5 (b^3-a^2) - 3k (a^2-b^3)

a^2-b^3 - (5*b^3-5*a^2) = a^2-b^3-5*b^3+5*a^2

-b^3-5*b^3=-6*b^3

a^2+5*a^2=6*a^2

3 * (a^2-b^3) = 3*a^2-3*b^3

(3*a^2-3*b^3) * k=3*a^2*k-3*b^3*k

6*a^2-6*b^3 - (3*a^2*k-3*b^3*k) = 6*a^2-6*b^3-3*a^2*k+3*b^3*k