Question

(x-3y)^4-27x+81y=???

Answer 1

(x-3y)⁴-27x+81y=(x-4y)⁴-27*(x-3y)=(x-3y)*((x-3y)³-27)=(x-3y)*((x-3y)³-3³)=
=(x-3y)*((x-3y-3)*((x-3y)²+(x-3y)*3+9)=(x-3y)*(x-3y-3)*(x²-6xy+9y²+3x-9y+9).