1) x+2- (x^2+4)/(x-2)=((x+2)(x-2)-x^2-4)/(x-2)=(x^2-4-x^2-4)/(x-2)=-8/(x-2)
2) (m-n)/(2mn)+2/(m-n)=((m-n)^2+4mn)/(2mn(m-n))=(m+b)^2/(2mn(m-n)) - возможно опечатка, не сокращается
3) (p+3)/(p+4)-(p-3)/(p-4)=((p+3)(p-4)-(p-3)(p+4))/(p-4)(p+4)=(p^2-p-12-p^2-p+12)/((p-4)(p+4))=-2p/((p-4)(p+4))
4) (7p+q)/(p^2-pq)+(p+7q)/(p^2-pq)=(7pq+q^2-p^2-pq)/(pq(p-q))=(q^2-p^2)/(pq(p-q))=-(p+q)/(pq)