5 /(х²+5х) + (х+15)/(25 - х²)= 5/ х(х+5)+ (х+15)/ (5-х)(5+х) = 25-5х+ х²+15х / х(х-5)(х+5)= х²+10х+25/ х(х-5)(х+5)= (х+5)²/ х(х-5)(х+5)= (х+5)/х(х-5)
1/(х+3)+ 9х/(х³+27)=1/(х+3) + 9х/ (х+3)(х²-3х+9)= (х²-3х+9+ 9х)/(х+3)(х²-3х+9)=
х²-6х+9/(х+3)(х²-3х+9)= (х-3)²/(х+3)(х²-3х+9)
2/х+ 12/(х²-6х)- (1-х)/(х-6)= 2/х+12/х(х-6)-(1-х)/(х-6)=( 2х-12+12 - х +х²)/х(х-6)=
(х²+х)/х(х-6)=х(х+1)х(х-6)= (х+1)/(х-6)
/- дробная черта