Lessons for G.CO.C.10
Isosceles and equilateral trianglesThe two angles opposite the congruent sides are congruent.Lesson
Indirect proofAssuming the opposite of what is to be shown and following it until something impossible appears.Lesson
Medians and altitudesA median joins a vertex to the midpoint of the opposite side.Lesson
Proving the base angles theoremAdding a bisector or a median to split an isosceles triangle into two congruent halves.Lesson
Proving the triangle angle sumDrawing a line through one vertex parallel to the opposite side and reading the angles off it.Lesson
Triangle angle sumThe three angles add to a straight line, and why.Lesson
Triangle centersEach family of special segments meets at one point, giving the triangle four classic centers.Lesson
Triangle inequalityAny two sides together are longer than the third.Lesson
Midsegments of triangles and trapezoidsThe segment joining two side midpoints is parallel to the third side and half as long.Lesson
Printable Worksheets
Isosceles and equilateral triangles worksheet (PDF)Printable worksheet with answer keyPreview
Indirect proof worksheet (PDF)Printable worksheet with answer keyPreview
Medians and altitudes worksheet (PDF)Printable worksheet with answer keyPreview
Proving the base angles theorem worksheet (PDF)Printable worksheet with answer keyPreview
Proving the triangle angle sum worksheet (PDF)Printable worksheet with answer keyPreview
Triangle angle sum worksheet (PDF)Printable worksheet with answer keyPreview
Triangle inequality worksheet (PDF)Printable worksheet with answer keyPreview
Midsegments of triangles and trapezoids worksheet (PDF)Printable worksheet with answer keyPreview