DOST Junior Level Science Scholarship (JLSS) Practice Exam

Any triangle drawn on a flat surface has interior angles that add up to a straight angle: 180 degrees. A helpful way to see this is to draw a line through the top vertex parallel to the base. The two angles at the base then correspond to the angles opposite the top vertex, so those three interior angles lie along a straight line. The total along that line is 180 degrees, so the interior angles must sum to 180 degrees. This holds for all triangles, not just a particular one. The other numbers would imply a different geometric situation, which doesn’t fit how angles inside a triangle arrange themselves.