(4) We commented that we thought that every spherical triangle should have angle sum bigger than 180. Show (intuitively) that the angle excess, the amount by which the angle-sum of a triangle is bigger than 180, is additive when triangles are placed side-by-side. That is, in the diagram below: A Show that D the angle excess of AABC is excess(AABC) = m/ABC + m2BCA +mZCAB - 180. excess(AADB) + excess(ADCB) = excess(ABC)