3
2a/(a-5)-5/(a+5)-2a²/[(a-5)(a=5)]=[2a(a+5)-5(a-5)-2a²]/[(a-5)(a+5)]=
=(2a²+10a-5a+25-2a²)/[(a-5)(a+5)]=(5a+25)/[(a-5)(a+5)]=5(a+5)/[(a-5)(a+5)]=
=5/(a-5)
4
(2x²+7x+9)/[(x-1)(x²+x+1)]+(4x+3)/(x²+x+1)-5/(x-1)=
[2x²+7x+9+(x-1)(4x+3)-5(x²+x+1)]/[(x-1)(x²+x=1)]=
(2x²+7x+9+4x²-4x+3x-3-5x²-5x-5)/[(x-1)(x²+x+1)]=
=(x²+x+1)/[(x-1)(x²+x+1)]=1/(x-1)
x=1,1 1/(1,1-1)=1/0,1=10