Answer:
b/x = (x + y)/b
where c = x + y then
b/x = c/b
Explanation:
Considering the larger of the three triangles the image represents,
b and a in light of the angle A form by both sides (the angle opposite the side a) would have a relationship
Cos A = x/b
hence b/x = 1/Cos A
Considering the largest triangle,
Cos A = b/(x +y)
hence,
(x + y)/b = 1/Cos A
as such,
b/x = (x + y)/b