The diagonals are equal and split a rectangle into four isosceles triangles. The diagonals ... 90°, then the smaller top left corner angle is 90° - 70° = 20°. Using the rectangle's lines ...

divide the sum of interior angles in a triangle by 3 In an isosceles triangle, two of the sides are equal. This means two of the angles are equal. These are the base angles. The base angles are ...

Students may notice symmetry in the isosceles and equilateral triangles and non-symmetry in the scalene triangles Informal recognition of these properties may be helpful in recognizing formal ...