A triangle has three vertices and three sides, where three angles of a triangle are formed at each vertex by a pair of adjacent sides. In a Euclidean space, the sum of measures of these three angles of any triangle is invariably equal to the straight angle, also expressed as 180°, π radians, two right angles, or a half-turn.

a. The three angles of a triangle can be arranged to form a ……….. angle.
b. The sum of three angles in a triangle is ………..