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Finding missing angles

Find the missing angle on a straight line.

Practice + answer key · 4 pages

Worksheet settings8 questions · 2 columns · A4
Known angle

Choose the given angle; the missing angle is its supplement to 180°.

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Finding missing anglesFinding missing angles. Practice. The marked angles form a straight line. Find x. The marked angles form a straight line. Find x. The marked angles form a straight line. Find x. The marked angles form a straight line. Find x.Name __________________________Date _______________Finding missing anglesFind x in each straight-angle diagram.Worked exampleTwo adjacent angles on a straight line are 65° and x. Find x. → 115°65° + x = 180°.1.The marked angles form a straightline. Find x.A straight line is divided by one ray into adjacent angles of 103° and x.103°x2.The marked angles form a straightline. Find x.A straight line is divided by one ray into adjacent angles of 105° and x.105°x3.The marked angles form a straightline. Find x.A straight line is divided by one ray into adjacent angles of 28° and x.28°x4.The marked angles form a straightline. Find x.A straight line is divided by one ray into adjacent angles of 27° and x.27°xMathSprig · mathsprig.site · support@mathsprig.sitePage 1 of 2mathsprig-1 · mathsprig-v1 · 4e56293f
Finding missing anglesFinding missing angles. Practice. The marked angles form a straight line. Find x. The marked angles form a straight line. Find x. The marked angles form a straight line. Find x. The marked angles form a straight line. Find x.Name __________________________Date _______________Finding missing anglesFind x in each straight-angle diagram.5.The marked angles form a straightline. Find x.A straight line is divided by one ray into adjacent angles of 67° and x.67°x6.The marked angles form a straightline. Find x.A straight line is divided by one ray into adjacent angles of 93° and x.93°x7.The marked angles form a straightline. Find x.A straight line is divided by one ray into adjacent angles of 103° and x.103°x8.The marked angles form a straightline. Find x.A straight line is divided by one ray into adjacent angles of 101° and x.101°xMathSprig · mathsprig.site · support@mathsprig.sitePage 2 of 2mathsprig-1 · mathsprig-v1 · 4e56293f
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Practice + answer key · 4 pages

Geometry

What you’ll practice

Find a missing adjacent angle on a straight line.

The two adjacent angles share a straight line, so they add to 180°. Subtract the angle you know to find the missing one.

How this skill works

A straight angle measures 180°.

The marked angles share the straight angle, so known + x = 180°. Subtract the known measure from 180°.

Worked example

Two adjacent angles on a straight line are 65° and x. Find x.
  1. 65° + x = 180°.
  2. x = 180° − 65° = 115°.

Answer: 115°

Teaching notes

  • Only add angles that make up the stated straight angle.
Practice questions
  1. The marked angles form a straight line. Find x.

    A straight line is divided by one ray into adjacent angles of 103° and x.

  2. The marked angles form a straight line. Find x.

    A straight line is divided by one ray into adjacent angles of 105° and x.

  3. The marked angles form a straight line. Find x.

    A straight line is divided by one ray into adjacent angles of 28° and x.

  4. The marked angles form a straight line. Find x.

    A straight line is divided by one ray into adjacent angles of 27° and x.

  5. The marked angles form a straight line. Find x.

    A straight line is divided by one ray into adjacent angles of 67° and x.

  6. The marked angles form a straight line. Find x.

    A straight line is divided by one ray into adjacent angles of 93° and x.

  7. The marked angles form a straight line. Find x.

    A straight line is divided by one ray into adjacent angles of 103° and x.

  8. The marked angles form a straight line. Find x.

    A straight line is divided by one ray into adjacent angles of 101° and x.

Answers and steps
  1. 77°
    1. A straight angle measures 180°, so 103° + x = 180°.
    2. x = 180° − 103° = 77°.
  2. 75°
    1. A straight angle measures 180°, so 105° + x = 180°.
    2. x = 180° − 105° = 75°.
  3. 152°
    1. A straight angle measures 180°, so 28° + x = 180°.
    2. x = 180° − 28° = 152°.
  4. 153°
    1. A straight angle measures 180°, so 27° + x = 180°.
    2. x = 180° − 27° = 153°.
  5. 113°
    1. A straight angle measures 180°, so 67° + x = 180°.
    2. x = 180° − 67° = 113°.
  6. 87°
    1. A straight angle measures 180°, so 93° + x = 180°.
    2. x = 180° − 93° = 87°.
  7. 77°
    1. A straight angle measures 180°, so 103° + x = 180°.
    2. x = 180° − 103° = 77°.
  8. 79°
    1. A straight angle measures 180°, so 101° + x = 180°.
    2. x = 180° − 101° = 79°.