1)25/(a²+5a+25)+2a/(a-5)+(a³+25a²)/(a-5)(a²+5a+25)=
=(25a-125+2a³+10a²+50a+a³+25a²)/(a-5)(a²+5a+25)=
=(3a³+35a²+75a-125)/(a-5)(a²+5a+25)
2)a-5 +15a/(a-5)=(a²-10a+25+15a)/(a-5)=(a²+5a+25)/(a-5)
3)(3a³+35a²+75a-125)/(a-5)(a²+5a+25)*(a²+5a+25)/(a-5)=(3a³+35a²+75a-125)/(a-5)²