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8th grade · Math · Unit 8 of 17

Angle Detective

Parallel lines and polygons

What your child practices

Using equal and supplementary angles when a transversal crosses parallel lines, and the angle sums of triangles, quadrilaterals and polygons, including exterior angles.

Maine Learning Results learning standard: 8.G.A.5 · angle sums of triangles and angles formed by parallel lines

How we explain it

Children can open this short lesson before they practice.

  1. Angles on a straight line add to 180°.
  2. The angles in a triangle add to 180°.
  3. When two lines cross, opposite angles are equal.

Example: Two angles on a straight line: one is 115°. What is the other? Together they make 180°. 180 − 115 = 65. Answer: 65°

Angle Detective in Maine

In the Maine Learning Results, this is unit 8 of 17 in 8th grade Math, after Tessellations & Transformations and before Tables, Graphs & Linear Relations.

Gradelings describes a child's practice on this unit as Beginning, Approaching, Meeting or Exceeding (Four practice steps). That reflects practice, not a report-card mark: the teacher decides the mark.

Source: Maine Department of Education

Sample questions

A taste of this unit. In the app, questions change every time and get easier or harder to match your child.

  1. Question 1

    An isosceles triangle has a top angle of 92°. What is each base angle?

    answer box°

  2. Question 2

    What is the sum of the interior angles of a polygon with 7 sides?

    answer box°

  3. Question 3

    Two co-interior angles between parallel lines measure (x + 20)° and (2x + 10)°. What is x?

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  4. Question 4

    What is the measure of each interior angle of a regular polygon with 6 sides?

    answer box°

  5. Question 5

    A transversal crosses two parallel lines. One angle measures 117°. How many degrees is a co-interior angle (on the same side of the transversal, between the lines) to it?

    answer box°

  6. Question 6

    What is the measure of each exterior angle of a regular polygon with 5 sides?

    answer box°

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