49
б)2/a-7/b=(2b-7a)/ab
г)
c/ab+a/cd=(c²d+a²b)/abcd
50б
5/a+(3a-5)/(a+1)=(5a+5+3a²-5a)/a(a+1)=(3a²+5)/[a(a+1)]
51
б)(a+1)/(a-1)+(a-1)/(a+1)=(a²+2a+1+a²-2a+1)/(a²-1)=(2a²+2)/(a²-1)
(a+1)/(a-1)-(a-1)/(a+1)=(a²+2a+1-a²+2a-1)/(a²-1)=4a/(a²-1)
г)m/(m+4)+m/(m-4)=[m(m-4+m+4)]/(m²-16)=2m²/(m²-16)
m/(m+4)-m/(m-4)=[m(m-4-m-4)]/(m²-16)=-8m/(m²-16)=8m/(16-m²)