G-CO.10

Prove theorems about triangles. Theorems include: measures of interior angles of a triangle sum to 180°; base angles of isosceles triangles are congruent; the segment joining midpoints of two sides of a triangle is parallel to the third side and half the length; the medians of a triangle meet at a point.

Khan Academy Resources

Getting ready for transformation propertiesTriangle angles reviewFinding angle measures between intersecting linesFinding angle measures using trianglesFind angles in trianglesAngle relationships with parallel linesEquation practice with anglesEquation practice with angle additionProve theorems using similarityFind angles in isosceles trianglesProve triangle propertiesAngles, parallel lines, & transversalsAngles in a triangle sum to 180° proofWorked example: Triangle angles (intersecting lines)Worked example: Triangle angles (diagram) Triangle exterior angle exampleProofs concerning isosceles trianglesIsosceles & equilateral triangles problemsProofs concerning equilateral trianglesExploring medial trianglesProving triangle medians intersect at a pointEquation practice with supplementary anglesEquation practice with vertical anglesMeasures of angles formed by a transversalMissing angles with a transversal

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