1
-(a-2)/(a+1)(a²-a+1)-(1-a)/(a²-a+1)=(-a+2-a+a²-1+a)/(a+1)(a²-a+1)=
=(a²-a+1)/(a+1)(a²-a+1)=1/(a+1)
2
(2m-20)/(m-2)(m+2)+4/(m-2)-6/m=(2m²-20m+4m+8-6m²+24)/m(m²-4)=
=(-4m²-16m+32)/m(m²-4)=-4(m²+4m-8)/m(m²-4)
3
(2m²-n²)/(m+n)(m²-mn+n²)-(m-n)/(m²-mn+n²)=
=(2m²+n²-m²+n²)/(m³+n³)=(m²+2n²)/(m³+n³)
4
1/(x+3)-(x²+18)/(x+3)(x²-3x+9)=(x²-3x+9-x²-18)/(x+3)(x²-3x+9)=
=(-3x-9)/(x+3)(x²-3x+9)=-3(x+3)/(x+3)(x²-3x+9)=-3/(x²-3x+9)