Exam Style Questions Ensure you have: Pencil, pen, ruler, protractor, pair of compasses and eraser You may use tracing paper if needed Guidance 1. Read each question carefully before you begin answering it. 2. Donʼt spend too long on one question. 3. Attempt every question. 4. Check your answers seem right. 5. Always show your workings ... 2 x ∠OBC + ∠COB = 180° (angle sum of triangle)  Obtuse ∠COB = 2 x ∠CAB (angle at centre twice angle at circumference)  ∠COB = 2 x ∠CBD; To prove ∠CAB = ∠CBD ∠OBC = ∠OCB (equal angles in isosceles triangle OBC) Construct the radii OB and OC; 2 x ∠OBC + ∠COB = 2(∠OBC + ∠CBD) (from  and  above)

Section 4 – 6: Isosceles Triangles Notes Isosceles Triangle: A triangle with at least _____ sides congruent. Isosceles Triangle Theorem: If two sides of a triangle are _____, then the angles opposite those sides are _____. Ex: Example #1: If DE CD, BC AC, and m CDE 120, what is the measure of BAC? “If a triangle is an isosceles triangle, then the median, angle bisector, and altitude will be the same segment.” #37. Triangle Sum Theorem – says that “If a polygon is a triangle, then its interior angles will measure a sum of 180 degrees.” #38.