1)с(5с-1)/(5с-1)²²4/[(5с-1)(5с+1)]=c/(5c-1)-4/[(5c-1)(5c+1)]=
=(5c²²+c-4)/[(5c-1)(5c+1)=(5c-4)(c+1)/[(5c-1)(5c+1)]
2)1-3/(5c-1)=(5c-1-3)/(5c-1)=(5c-4)/(5c-1)
3)(5c-4)(c+1)/[(5c-1)(5c+1):(5c-4)/(5c-1)=
=(5c-4)(c+1)/[(5c-1)(5c+1)]*(5c-1)/(5c-4)=(c+1)/(5c+1)
4)(c+1)/(5c+1)-c/(5c+1)=(c+1-c)/(5c+1)=1/(5c+1)