Hi,

we use de notations ABC with alpha, betha, gamma, a,b,c

From Sinus Formula we have:

sin(alpha)/a=sin(betha)/b => b=a*sin(betha)/sin(alpha)

=>

(a+b)/(a-b)=[(a+a*sin(betha)/sin(alpha)] / )=[(a-a*sin(betha)/sin(alpha)] =

(sin(alpha)+sin(betha))/(sin(alpha)-sin(betha))

for begin.