Geometry
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What this topic is really about
According to Thales's theorem, any angle inscribed in a semicircle that subtends the diameter is always a right angle, or 90 degrees. Option D is incorrect because 180 degrees is the measure of the straight angle at the center of the circle, not the inscribed boundary angle.
The perimeter, or circumference, of a circle is calculated using the formula C = pi * d. Substituting the diameter of 14 cm and pi as 22/7 yields 44 cm. Option D is incorrect because 154 represents the circle's area, calculated as pi * r^2, rather than its perimeter.
See the mechanism
According to Thales's theorem, any angle inscribed in a semicircle that subtends the diameter is always a right angle, or 90 degrees. A diagram for this topic isn't available yet — the worked example below walks the same reasoning step by step.
An exam-style question, fully explained
Angle in a semicircle is always:
- Identify what the question tests: Angle in a semicircle is always:.
- According to Thales's theorem, any angle inscribed in a semicircle that subtends the diameter is always a right angle, or 90 degrees.
- Option D is incorrect because 180 degrees is the measure of the straight angle at the center of the circle, not the inscribed boundary angle.
Traps the examiner sets
- Option D is incorrect because 180 degrees is the measure of the straight angle at the center of the circle, not the inscribed boundary angle.
- Option D is incorrect because 154 represents the circle's area, calculated as pi * r^2, rather than its perimeter.
Test your recall
Answer each from memory — you'll see instantly whether you're right and why.
Run a focused 10-question mini-mock on Geometry and see it stick.
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