Definition of a Median of a Triangle A median of a triangle is a segment whose endpoints are a vertex and a midpoint of the opposite side
Just to make sure we are clear about what an opposite side is….. Given ABC, identify the opposite side of A. of B. of C. BC AC AB
Any triangle has three medians. B Any triangle has three medians. L M A N C Let L, M and N be the midpoints of AB, BC and AC respectively. CL, AM and NB are medians of ABC.
Where 3 or more lines intersect A new term… Point of concurrency Where 3 or more lines intersect
Centroid Centroid The point where all 3 medians intersect Is the point of concurrency
The centroid is the center of balance for the triangle. You can balance a triangle on the tip of your pencil if you place the tip on the centroid
Centroid Theorem The centroid of a triangle divides the median into segments with a 2:1 ratio. The distance from the vertex to the centroid is twice the distance from the centroid to the midpoint.
VERTEX 3x 2x CENTROID x MIDPOINT
The distance from the vertex to the centroid is two-thirds Centroid Theorem The distance from the vertex to the centroid is two-thirds the distance from the vertex to the midpoint
𝟐 𝟑 QC = QZ QC = 2CZ
PY = 21 PC = CY = 8 12 4 8 8 6
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MID-SEGMENTS OF A TRIANGLE A mid-segment of a triangle connects the midpoints of two sides of the triangle.
Mid-segment Theorem The midsegment of a triangle is parallel to the third side and is half as long as that side. D B C E A
Identify the 3 pairs of parallel lines shown above
The mid-segment of a triangle is parallel to the third side and is half as long as that side. y y 2x x z z
2b. 2a.
Example 1 In the diagram, ST and TU are midsegments of triangle PQR. Find PR and TU. 5 ft 16 ft TU = ________ PR = ________
Example 3 In the diagram, ED and DF are midsegments of triangle ABC. Find DF and AB. 3X – 4 5X+2 2 (DF ) = AB 2 (3x – 4 ) = 5x + 2 6x – 8 = 5x + 2 x – 8 = 2 x = 10 x = ________ 10 DF = ________ 26 AB = ________ 52
ED is a mid-segment of ABC
Altitude .. Angle Bisector.. Perpendicular Bisector… Median .. Quick notes Angle Bisector.. Angle into 2 equal angles .. Incenter Perpendicular Bisector… 90° .. bisects side .. Circumcenter Median .. Vertex .. Midpoint of side ..Centroid Altitude .. Vertex .. 90° .. Orthocenter