Докажите справедливость равенства
1.(a+x)³-a(a+x)²- x²(2a+1)=a²x
2.(a-1)³+3(a-1)²+3(a-1)+1=a³
3.(x³+y³)²-(x²+y²)³+3x²y²(x+y)²=8x³y³
4.(m-3n)³-(2m-3n)(3mn+(m-3n)²)=-m³