12) (a^2+b^2-c^2+2ab)/ (a^2-b^2+c^2+2ac)=((a+b)^2-c^2 )/( (a+c)^2-b^2) = ( (a-b-c) . (a+b+c)) /((a+c-b) .(a+c+b))=(a+b-c)/(a+c-b) 13)(m^2-n^2-2np-p^2)/(m^2-2mn+n^2-p^2) = ((m^2-(n+p)^2)/(m^2-2mn+n^2)-p^2)= (m-n-p)(.m+n+p)/(m-n-p) (m-n+p)= (m+n+p)/(m+p-n) .