Find the quadratic form Q(x,y) for which Q(3,5)=Q(4,7)=Q(7,12)=1 by first drawing a strip in the Farey diagram containing the triangles ⟨1/0,0/1,1/1⟩ and ⟨3/5,4/7,7/12⟩ (this can be done using the continued fraction for 7/12), then adding the edges of the dual tree that meet these triangles, then filling in values of the topograph starting with the given values.