Parallel Lines and the Triangle Angle Sum Theorem

Parallel Lines and the Triangle Angle Sum Theorem Geometry 3 -3

• Exterior Angle – The angle formed outside the triangle, and along a side as shown Exterior Angle Triangle Term

• Exterior Angle – Exterior Angle Triangle Term

• Exterior Angle – Six different exterior angles can be formed for a triangle Exterior Angle Triangle Term

• Supplies • Scissors • Printer Paper • Draw two different shaped triangles with a ruler (be creative) • Cut them out with a scissors Investigation

• With ONE of the triangles, tear off the corners of the triangles • Arrange the angles so they are adjacent • What do you observe? Investigation

• With the remaining triangle, tear off two corners of the triangles • Arrange the torn corners in the place of an exterior angle to the remaining angle • What do you observe? Investigation

• Triangle Sum Theorem The sum of the measure of the interior angles of a triangle is 180° What we have learned

• Triangle Sum Theorem How can this be proven with parallel lines? y° Z° Alternate Interior Angles What we have learned

• Exterior Angle Theorem The measure of an exterior angle of a triangle is equal to the measure of the two non-adjacent interior angles What we have learned

Practice Problems

m 1=75° m 2=55° m 3=55° m 4=40° m 5=140° m 6=40° m 7=75° m 8=65° m 9=115°

X=23 Exterior Angle = 100°

m t = 62° m v = 118° m w = 37°

• Pages 135 – 138 • 6 – 11, 16 – 22 even, 27, 28, 33, 36, 49 Homework