Interior angles of a triangle

Task goals

• Find a missing angle in a scalene, isosceles, equilateral, or right-angled triangle from a labelled diagram, using the 180-degree angle sum.
• Use the equal base angles of an isosceles triangle to find both remaining angles from one given angle.
• Explain why every equilateral triangle has three 60-degree angles.
• Set up and solve an equation when one or more interior angles are given as an algebraic expression.
• Find all three angles when they are given as a ratio, and name the triangle using angle language.
• Decide whether a given set of angles can form a triangle, and explain an incorrect claim using the angle-sum rule.