ChalkHour

Year 7 Maths: Angles on a straight line lesson pack

A complete, ready-to-teach KS3 lesson on angles on a straight line. Below is a real sample of what ChalkHour makes: the full pack adds three levels of worksheet, model answers, a teaching explainer and print-ready PDF and Word files.

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Real sample

Angles on a Straight Line

This lesson introduces Year 7 students to the geometric property that angles meeting at a point on a straight line sum to 180 degrees. It moves from simple subtraction to solving for variables (x) in algebraic contexts.

Learning objectives

  • Recall that angles on a straight line sum to 180 degrees.
  • Calculate missing angles on a straight line by subtracting known values from 180.
  • Solve algebraic equations to find missing angles on a straight line.
  • Apply angle facts to solve multi-step geometric problems.

Lesson plan (60 minutes)

  1. Starter · 5 min

    Do Now: Mental arithmetic and revision of acute/obtuse angle definitions.

  2. Introduction · 10 min

    Direct Instruction: Explaining the 180° rule, vocabulary, and modeling the calculation steps.

  3. Guided Practice · 10 min

    Guided Practice: Interactive whiteboards - solving 3 basic problems together.

  4. Main Activity · 25 min

    Independent Practice: Students work through Support, Core, or Stretch worksheets.

  5. Review · 10 min

    Plenary: Multiple-choice quiz to check for misconceptions and summary of learning.

Key vocabulary

Straight Line
A line that is perfectly flat, measuring 180 degrees.
Degree (°)
A unit of measurement for angles.
Supplementary Angles
Two or more angles that add up to 180 degrees.
Right Angle
An angle that is exactly 90 degrees, often marked with a square.
Vertex
The point where two or more lines meet.

Core worksheet (first questions)

  1. A straight line is divided into two angles: 42° and a. Find a.
  2. Calculate the missing angle if one angle is 123°.
  3. A straight line has three angles: a right angle, 48°, and b. Find b.
  4. Find x if the two angles on a line are x and 155°.

Quiz (sample)

  1. 1. What is the sum of angles on a straight line?

    • A. 90°
    • B. 180°
    • C. 270°
    • D. 360°

  2. 2. If one angle on a straight line is 50°, what is the other angle?

    • A. 40°
    • B. 50°
    • C. 130°
    • D. 140°

  3. 3. What is the mathematical term for two angles that add up to 180°?

    • A. Complementary
    • B. Supplementary
    • C. Adjacent
    • D. Reflex

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