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 ...

A scalene triangle with angles of 50°, 60° and 70° is an acute-angled triangle. An isosceles triangle with angles of 90°, 45° and 45° is a right-angled triangle. This is the only combination ...

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 ...