...a triangle's congruency in the case ASA, SAS, SSA, AAS...
Do all oblique cylinders have two congruent circles as bases? Find the (acute) angle theta between the planes x + \sqrt3 z = 3 and -3/4 x + \sqrt3 / 2 y - 3\sqrt3/ 4 z = 4. What is a quadrilateral with four sides and is convex? ...