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# Medians & altitudes of a triangle

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Medians and Altitudes of Triangles

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### Medians & altitudes of a triangle

1. 1. MEDIANS AND ALTITUDES OF A TRIANGLE B E D G A F E
2. 2. MEDIANS OF A TRIANGLEA median of a triangle A is a segments whose endpoints are a vertex of the triangle and the MEDIAN midpoint of the opposite side. In the figure, in ∆ ABC , shown at the right, D is the midpoint of side BC . So, segment AD C is a median of the D B triangle 2
3. 3. CENTROIDS OF THE TRIANGLEThe three medians of a triangle are concurrent. This means that they meet at a point. The point of concurrency is called the CENTROID OF THE TRIANGLE. CENTROID The centroid, labeled P P in the diagrams in the next few slides are ALWAYS inside the triangle. acute triangle 3
4. 4. CENTROIDS P centroid P centroidRIGHT TRIANGLE obtuse triangle You see that the centroid is ALWAYS INSIDE THE TRIANGLE 4
5. 5. T H E ORE M : C ON C URRE NC Y OF M E DI ANS OF A T RI A NG LEThe medians of a triangle intersect at a B point that is two thirds of the distance from D each vertex to the midpoint of the opposite side. E CIf P is the centroid of P ∆ABC, then FAP = 2/3 AD,BP = 2/3 BF, and ACP = 2/3 CE 5
6. 6. EXERCISE: USING THE CENTROID OF ATRIANGLEP is the centroid of ∆QRS shown below R and PT = 5. Find RT and RP. S P T Q 6
7. 7. EXERCISE: USING THE CENTROID OF A TRIANGLEBecause P is the centroid. RP = 2/3 R RT.Then PT= RT – RP = 1/3 RT.Substituting 5 for PT, S 5 = 1/3 RT, so P RT = 15. TThen RP = 2/3 RT = Q2/3 (15) = 10► So, RP = 10, and RT = 15. 7
8. 8. EXERCISE: FINDING THE CENTROID OF A TRIANGLE J (7, 10) The coordinates of N are: 10 3+7 , 6+10 = 10 , 16 2 2 2 2 8 N Or (5, 8) 6 L (3, 6) P Find the distance from vertex K to midpoint N. 4 The distance from K(5, M 2) to N (5, 8) is 8-2 or 6 units. 2 K (5, 2) 8
9. 9. EXERCISE: DRAWING ALTITUDES AND ORTHOCENTERS Where is the orthocenter located in each type of triangle?a. Acute triangleb. Right trianglec. Obtuse triangle 9
10. 10. ACUTE TRIANGLE - ORTHOCENTER B E D G A F E∆ABC is an acute triangle. The three altitudesintersect at G, a point INSIDE the triangle. 10
11. 11. RIGHT TRIANGLE - ORTHOCENTER ∆KLM is a right triangle. The two K legs, LM and KM, are also altitudes. J They intersect at the triangle’s right angle. This implies that the orthocenter M L is ON the triangle at M, the vertex of the right angle of thetriangle. 11
12. 12. OBTUSE TRIANGLE - ORTHOCENTER P Z W Y Q X R∆YPR is an obtuse triangle. The three lines that contain the altitudes intersect at W, a point that is OUTSIDE the triangle. 12
13. 13. CONCURRENCY OF ALTITUDES OF A TRIANGLE F B H A E D CThe lines containing the altitudes of a triangle are concurrent.If AE, BF, and CD are altitudes of ∆ABC, then the lines AE, BF, and CD intersect at some point H. 13