SOLVED: Definition: In neutral geometry, the defect of a triangle is defined to be 180 minus the angle sum of the triangle. Given a triangle ABC, we denote its defect by d(ABC).Definition: In neutral geometry, the defect of a convex quadrilateral is defined to be 360 minus the angle sum of the quadrilateral. Given quadrilateral ABCD, we denote its defect by d(ABCD).