You can determine angles around straight lines by employing pattern-spotting, logic, and reasoning.
Key facts to remember:
One half turn is 180°. When a straight line or half turn is split into two angles, knowing one angle enables the calculation of the other.
For instance, 120° + 60° = 180°.
If a straight line was divided into three angles, the sum of all three angles would be 180°.
Various examples of angles on straight lines illustrate how they sum up to 180°.
Example: Can you work out what angle b is?
Sol:
Angle b, when on a straight line with 140°, must be 40°.
140° + 40° = 180°
For angle c, since b + c = 180°, and b is 40°, c equals 140°.
40° + 140° = 180°
Angle d is 40° as it's on a straight line with c.
c + d = 180°
Example: What do you think angle c is in both of these diagrams?
In the first diagram angle c equals 70° and in the second diagram angle c equals 145°.
Angles b and d are vertically opposite, so they are equal too.
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1. What are the different types of angles? |
2. How do you calculate the measure of an angle? |
3. How can angles be classified based on their relationship to each other? |
4. What is the sum of interior angles in a triangle? |
5. How can you use angle properties to solve geometry problems? |
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