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WHS Chapter 5 Properties/Attributes of Triangles

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Term
Definition
acute triangle   triangle with all three angles < 90°  
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right triangle   triangle with one 90° angle  
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obtuse triangle   triangle with one angle > 90°  
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angle bisector   a line or ray that divides an angle into two congruent angles  
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conclusion   the phrase following the word 'then' in a conditional statement  
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leg of a right triangle   one of the two sides that form the right angle in a right triangle  
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perpendicular bisector of a segment   a line that is perpendicular to a segment at its midpoint  
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altitude of a triangle   a perpendicular segment from a vertex to the line containing the opposite side  
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centroid of a triangle   the point of concurrency of the three medians of a triangle; also known as the center of gravity  
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circumcenter of a triangle   the point of concurrency of the perpendicular bisectors of a triangle  
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concurrent   three or more lines that intersect at one point  
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equidistant   the same distance from two or more objects  
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incenter of a triangle   the point of concurrency of the three angle bisectors of a triangle  
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median of a triangle   a segment whose endpoints are a vertex of the triangle and the midpoint of the opposite side  
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midsegment of a triangle   a segment that joins the midpoints of two sides of the triangle  
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orthocenter of a triangle   the point of concurrency of the three altitudes of a triangle  
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polygon   a closed plane figure formed by three or more line segments  
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bisect   cuts or divides something into two equal parts  
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slope   the measure of the steepness of a line  
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intersection   the set of points that two or more lines have in common  
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trinomial   polynomial with 3 terms  
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equiangular triangle   triangle with three equal measures  
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perimeter   distance around a figure  
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deductive reasoning   using logic to draw conclusions from facts, definitions, and properties  
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circumference   distance around a circle  
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coplanar   points in the same plane  
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translation   movement across a plane  
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midsegment triangle   the triangle formed by the three midsegments of a triangle  
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locus   a set of points that satisfies a given condition  
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Perpendicular Bisector Theorem   If a point is on the perpendicular bisector of a segment, then it is equidistant from the endpoints of the segment  
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Converse of the Perpendicular Bisector Theorem   If a point is equidistant from the endpoints of a segment, then it is on the perpendicular bisector of the segment.  
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Angle Bisector Theorem   If a point is on the bisector of an angle, then it is equidistant from the sides of the angle.  
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Converse of the Angle Bisector Theorem   If a point in the interior of an angle is equidistant from the sides of the angle, then it is on the bisector of the angle.  
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point of concurrency   a point where three or more lines coincide  
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Circumcenter Theorem   The circumcenter of a triangle is equidistant from the vertices of the triangle.  
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inscribed   When a circle in a polygon intersects each line that contains a side of the polygon at exactly one point  
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circumscribed   when a circle contains all the vertices of a polygon  
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Incenter Theorem   The incenter of a triangle is equidistant from the sides of the triangle.  
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Centroid Theorem   The centroid of a triangle is located ⅔ of the distance from each vertex to the midpoint of the opposite side.  
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Triangle Midsegment Theorem   A midsegment of a triangle is parallel to a side of the triangle, and its length is half the length of that side.  
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indirect proof   Begin by assuming that the conclusion is false. Then show that this assumption leads to a contradiction. Also known as a "proof by contradiction".  
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Angle-Side Relationships in Triangles - Theorem 1   If two sides of a triangle are not congruent, then the larger angle is opposite the longer side.  
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Angle-Side Relationships in Triangles - Theorem 2   If two angles of a triangle are not congruent, then the longer side is opposite the larger angle.  
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Triangle Inequality Theorem   The sum of any two side lengths of a triangle is greater than the third side length.  
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Pythagorean Theorem   In a right triangle, the sum of the squares of the lengths of the legs equals the square of the length of the hypotenuse.  
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Converse of the Pythagorean Theorem   If the sum of the squares of the lengths of two sides of a triangle is equal to the square of the length of the third side, then the triangle is a right triangle.  
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Pythagorean Inequalities Theorem   In ∆ABC , 'c' is the longest side. If c² > a² + b², the ∆ABC is an obtuse triangle. If c² < a² + b², then ∆ABC is an acute triangle.  
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45°-45°-90° Triangle Theorem   In a 45°-45°-90° triangle, both legs are congruent, and the length of the hypotenuse is the length of a leg times √2.  
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30°-60°-90° Triangle Theorem   In a 30°-60°-90° triangle, the length of the hypotenuse is 2 times the length of the shorter leg, and the length of the longer leg is the length of the shorter leg times √3.  
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