2Perpendicular bisector: line that cuts a segment into two equal parts which measure 90. Converse: if a point is equidistant from the endpoints of a segment, then it is on the perpendicular bisector of the segment.Examples:AB is the perpendicular bisector of CDFE is perpendicular bisector of IHMN is perpendicular bisector of lkafcdhiMbeLKN
3dbAngle bisector: divides an angle into two equal partsThe angle bisector in this example is AB which bisects <DAC .acAngle bisector theorem: the angle bisected in a triangle will have the same measure as the other half of the triangle.Measure of triangle ABD is = to measure of triangleCBD because of BD which is the angle bisector ofABCABCD
4Three or more lines are concurrent if they intersect a single point. Concurrency of Perpendicular Bisectors of a Triangle Theorem: The perpendicular bisectors of a triangle intersect at a point that is equidistant from the vertices of the triangleCircumcenter: the center of a circle that circumscribes a triangle.
5Concurrency of Angle Bisectors of a Triangle Theorem: The angle bisectors of a triangle intersect at a point that is equidistant from the sides of the triangle.The incenter of a triangle is equidistant from all sides of the triangle.
6A median is a line joining the vertex to the midpoint of the opposite side. The centroid is the point of congruency of the three medians of the triangle.Acute triangle right triangle obtuse triangleconcurrency of Medians of a Triangle Theorem: The medians of a triangle intersect at a point that is two thirds of the distance from each vertex to the midpoint of the opposite side
7Altitude of a triangle is where the lines of a triangle intersect The orthocenter is the intersection of three altitudes of a triangle.Concurrency of Altitudes of a Triangle Theorem: The lines containing the altitudes of a triangle are concurrent
8a midsegment is parallel to the third part of a triangle and is half the length of the third side 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 side510
9The relationship between the sides and the angles are that, the opposite side of the shortest angle will be the shortest side, and the opposite side of the largest angle will be the largest side.In this example we can see that segment BC is the smallest because the measure of angle A is the smallest904050ABCshortest80406075longestshortest5550
10Exterior angle inequality: The measure of an exterior angle of a triangle is greater than the measure of either remote interior angle.<ABC will always be greater than BAD.ADBcmhlkipno
11Triangle inequality theorem: Any side of a triangle is always shorter than the sum of the other two sides .ABCould a triangle have sides of4, 8, 2?And can you make a triangle with 5,6,7?Ca + b > c b + c > a a + c > b
12Indirect proof: to write an indirect proof you have to assume that the given is true, then stop when the given contradicts itself.Examples:Statement reason<BDA is a gvenStraight angleM<BDA= def of straight angleAD is perpendicularBisector of BC given<BDA is rightangle def of perpendicularM<BDA= def. of right angleM<BDA is not a straight angle!ABCD
13Prove that triangles cant have 2 right angles StatementAssume angle A ans <B are right trianglesMeasure of <A=90 and m<B=90Measure of <A+<B+<C= 18090+90+<C=180Measure of <C=0<A and <B cannot be right anglesReasonGivenDefinition of right anglesSum of anglesSubstitutionSubtractioncontradiction
14Hinge theorem: 2 triangles have 2 sides that are congruent, but the 3 sides is not congruent, then the triangle with the larger included angle has the longer side.FEF < GFBy the hinge theorem82EGH