TRIANGLES. TRIANGLES. AND MORE TRIANGLES. Menu options ahead. Full screen to listen to music Option #1 What is it? A line that bisects a segment and is perpendicular to that same segment. * Any point that is on the perpendicular bisector is equidistant to both of the endpoints of the segment which is perpendicular to. Converse: *If the point is equidistant from both of the endpoints of the segment, then it is a perpendicular bisector. THEOREM: Extra: A perpendicular bisector is the locus of all points in a plane that are equidistant from the endpoints of a segment. Segment Perpendicular bisector Are both congruent. 7cm a b cm d 1. Given that AC= 25.5, BD=20, and BC= Find AB. AB= Given that m is the perpendicular bisector of AB and BC= 30. Find AC. AC= 30 3.Given that m is the perpendicular bisector of AB, AC= 4a, and BC= 2a+26. Find BC. 2a+26=4a -2a=-26 a=13 plug in both equations BC= 52 Option #2 What is it? A ray or any line that cuts an angle into two congruent angles. Theorem : * Any point that lies on the angle bisector is equidistant to both of the sides of the angle. Converse: * If it is equidistant to both sides of the angle, then it lies on the angle bisector. MUST: the point always has to lie on the interior of the angle. Angle point that Angle bisector lies on the bisector is equidistant to both sides of the angle 1.5 cm A D C B 1.Given that BD bisects ABC and CD = 21, find AD. AD= Given that AD =65, CD= 65 and mABC = 50 , find m CBD. m DBC = 25 3. Given that DA=DC, m DBC= (10y+3) , and m DBA= (8y+10) , find mDBC. 10y+3=8y+10 2y+3=10 2y=7y=3.5 plug in both equations. mDBC=38 Option #3 example. G is the point of concurrency. It is the point where all the 3 perpendicular bisectors of a triangle meet. What makes it special? It is the point of concurrency and it is equidistant to all 3 vertices. EXAMPLE F is the circumcenter in this equilateral triangle. The circumcenter is on the inside of the triangle. 1. Knowing what circumcenter is, it would help you if you are a business person to know a strategic place in between 3 cities to place your business. That way it would be located in the same distance from all 3 cities for customers to come. f d 2.In an acute the circumcenter is on the inside of the triangle C is the circumcenter 3.In a right the circumcenter is on the midpoint of the hypotenuse D is the circumcenter 4.In an obtuse the circumcenter is on the outside of the triangle. F is the circumcenter c The angle bisectors of a triangle meet at a point that is equidistant from the three sides of the triangle. 1.What is the distance from H to G, if F to H is 10 cm? 10cm from H to G 2. H to E is 15cm, then what would be H to G doubled? Real: H to G would be 15cm and doubled would be 30cm 3.H in this triangle is what? The incenter of triangle ABC The point of concurrency where the three angle bisectors of a triangle meet. It is equidistant (same distance) from each three sides of the triangle EXAMPLES: G. H K LJ M P 1. P is the incenter 2. If you want to open a new restaurant in town you have to place it at the incenter of three major highways so people can go to your restaurant. TRIANGLE 3. If the distance from K to P is 2cm, what is the distance from P to L? From P to L = 2cm Option #4 Median Is the segment that goes from the vertex of a triangle to the opposite midpoint Ex.1 : Median Ex.3 : Ex. 2: all medians are congruent. Shown in yellow The point where the medians of a triangle intersect. Is the center of balance. The distance from the vertex to the centroid is the double the distance from the centroid to the opposite side. EXAMPLES: 1. Balance a triangular piece of glass on a triangular coffee table. 2. G is the centroid. 3. b y p x a z c AP= 2/3 AY BP=2/3BZ CP=2/3CX The medians of a triangle intersect at a point that is 2/3 of the distance from each vertex to the midpoint of the opposite side Option #5 A segment that goes from the vertex perpendicular to the line containing the opposite side. Where the altitudes of a triangle intersect. altitude hypotenuse TRIANGLES !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! Concurrency of Altitudes of a Triangle Theorem The lines containing the altitudes of a triangle are concurrent Option #6 A segment that joins the midpoints of two sides of the triangle. Every triangle has 3midsegments that form the midsegment triangle. Midsegment Theorem The segment joining the midpoints of two sides of a triangle is parallel to the third side, and is half the length of the third side. Option #7 In any triangle the longest side is always opposite from the largest angle. The small side is opposite from a small angle. EXAMPLES: Option #8 The exterior angle is bigger (grater) than the non-adjacent interior angles of the triangle. Triangle Inequality Theorem The sum of the lengths of two sides of a triangle is greater than the length of the third side. Triangle Inequality Theorem The sum of the lengths of two sides of a triangle is greater than the length of the third side. TELL WHEATHER A TRIANGLE CAN HAVE THE SIDES WITH THE GIVEN LENGTHS. EXPLAIN 1.3,5,7 2. 4, 6.5, , 4, > > > 7 8>7 10.5>119>7 YES, the sum of each NO. by the 3 rd triangleYes, 5+4 is grater than 7 so Pair of the lengths is inequality thm. A trianglethere can be a triangle. Grater than the 3 rd