Find missing angles in triangles and quadrilaterals

Learning Objectives Recall that the sum of interior angles is 180° for a triangle and 360° for a quadrilateral. Calculate a single missing angle in a triangle given the other two angles. Calculate a single missing angle in a quadrilateral given the other three angles. Set up and solve linear equations to find angle measures represented by algebraic expressions. Apply the properties of special triangles (isosceles, equilateral, right) to determine unknown angles. Apply the properties of special quadrilaterals (parallelograms) to determine unknown angles. Ever wonder how architects design stable bridges or how game developers create realistic 3D worlds? 📐 It all starts with understanding the fundamental rules of angles! In this tutorial, you will learn the core principles th...

TermDefinitionExample Interior AnglesThe angles located on the inside of a polygon, formed by two adjacent sides.A triangle has three interior angles, one at each vertex (corner). TriangleA polygon with three sides and three interior angles.A shape with vertices A, B, and C, and angles ∠A, ∠B, and ∠C. QuadrilateralA polygon with four sides and four interior angles.A square, rectangle, trapezoid, or parallelogram. Isosceles TriangleA triangle that has two sides of equal length. The angles opposite the equal sides are also equal.A triangle with angles measuring 70°, 70°, and 40°. Equilateral TriangleA triangle that has all three sides of equal length. All three of its interior angles are equal, each measuring 60°.A triangle with angles measuring 60°, 60°, and 60°. ParallelogramA quadrilater...

Triangle Angle Sum Theorem \angle A + \angle B + \angle C = 180^{\circ} The sum of the measures of the three interior angles of any triangle is always 180 degrees. Use this to find a missing angle when you know the other two. Quadrilateral Angle Sum Theorem \angle A + \angle B + \angle C + \angle D = 360^{\circ} The sum of the measures of the four interior angles of any quadrilateral is always 360 degrees. Use this to find a missing angle when you know the other three.