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7th grade · Math · Unit 15 of 18

Angle Relationships

Complementary, supplementary, vertical

What your child practices

Using complementary, supplementary, vertical and adjacent angles to find a missing angle, sometimes with a simple equation.

Alabama Course of Study content standard: 7.21 · using supplementary, complementary, vertical and adjacent angles to find unknown angles

How we explain it

Children can open this short lesson before they practice.

  1. Complementary angles add to 90°. Supplementary angles add to 180°.
  2. Vertical angles (opposite when lines cross) are equal.
  3. Write an equation and solve for the missing angle.

Example: Two angles are supplementary. One is 65°. What is the other? 180 − 65 = 115. Answer: 115°

Angle Relationships in Alabama

In the Alabama Course of Study, this is unit 15 of 18 in 7th grade Math, after Proportional Relationships and before Samples & Populations.

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: Alabama State Department of Education (ALSDE)

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

    Two lines cross. One angle is 91°. What is the angle vertically opposite to it?

    • 269°
    • 94°
    • 91°
    • 89°

  2. Question 2

    Two angles are complementary. One is x and the other is 2x. What is x?

    • 40°
    • 30°
    • 45°
    • 60°

  3. Question 3

    Two angles are supplementary. One is 26°. What is the other?

    • 26°
    • 154°
    • 153°
    • 64°

  4. Question 4

    Three angles sit side by side on a straight line. Two of them are 56° and 63°. What is the third?

    • 119°
    • 61°
    • 241°
    • 34°

  5. Question 5

    Two angles are supplementary. One is x and the other is 4x. What is x?

    • 46°
    • 45°
    • 36°
    • 144°

  6. Question 6

    Two angles are complementary. One is 69°. What is the other?

    • 22°
    • 69°
    • 111°
    • 21°

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