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MathidiaMathematics Academy
Angles and constructions
Lesson 57 of 75
Easy practice

Angles at a point and on a line

Objective. Use 360° at a point and 180° on a straight line.

  1. 1. Learn
  2. 2. Worked example
  3. 3. Practice
  4. 4. Feedback
  5. 5. Continue

Learn: the key idea

Angles at a point and on a line is built on a small number of dependable facts. Reason with angle facts and create accurate geometric drawings. Represent the information first, choose a method deliberately, show each step and use an inverse operation or estimate to check that the result fits the question.

Worked example

Angles on a line are 45° and x. Find x.

45
Illustrated card showing 45
  1. 1Identify the mathematical information and what must be found.
  2. 2Represent it with a number line, diagram, table or expression where helpful.
  3. 3Apply the relevant fact carefully and keep each line clear.
  4. 4Check the result against the conditions in the question: 135°.

Answer: 135°

Concept mastery

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Practice

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Common mistake. A common mistake in angles at a point and on a line is to apply a remembered procedure before reading the signs, units or order carefully. Write the structure first, then calculate and check.

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