А
(x-9)/[(x-3)(x+3)]+3/[x(x-3)]=(x²-9x+3x+9)/[x(x²-9)]=(x²-6x+9)/[x(x²-9)]=
=(x-3)²/[x(x-3)(x+3)]=(x-3)/[x(x+3)]
б
1/(x-2)-6x/[(x-2)(x²+2x+4)]=(x²+2x+4-6x)/(x³-8)=(x²-4x+4)/(x³-8)=
=(x-2)²/[(x-2)(x²+2x=4)]=(x-2)/(x²+2x+4)
в
3/x+21/[x(x-7)]-(4-x)/(x-7)=(3x-21+21-4x+x²)/[x(x-7)]=(x²-x)/[x(x-7)]=
=x(x-1)/[x(x-7)]=(x-1)/(x-7)