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| 8.3 |
Angles related to Parallel Lines and Transversals |
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| Parallel lines: |
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| Definition |
- Parallel lines will not intersect with each other.
- Parallel lines can be denoted using arrowheads as shown in the diagram below.
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| Transversal: |
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| Definition |
- A straight line that intersects two or more straight lines.
- The diagram below shows that \(PQ\) is a transversal.
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| The corresponding angles, alternate angles and interior angles: |
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(i) Corresponding angles
- The corresponding angles are equal where \(\angle a=\angle b\).
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(ii) Alternate angles
- The alternate angles are equal where \(\angle b=\angle c\).
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(iii) Interior angles
- The sum of the interior angles is \(180^\circ\) where \(\angle c+\angle d=180^\circ\).
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| Angles of elevation and depression: |
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| (i) Angle of elevation |
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| Definition |
- When a person sees an object which is at a higher level, the angle between the line of sight and the horizontal line is known as the angle of elevation.
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Form the diagram above, angle \(a\) is the angle of elevation of the bird from the sight of the boy.
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| (ii) Angle of Depression |
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| Definition |
- When a person sees an object which is at a lower level, the angle between the line of sight and the horizontal line is known as the angle of depression.
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Form the diagram above, angle \(b\) is the angle of depression of the cat from the sight of the girl.
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