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Key Stage 3 Geometry
Circles
Use radius, diameter, circumference and area of circles.
Key idea
Mark the diagram, name the fact you are using, and calculate from known angles, lengths or measures.
What you will learn
Use radius confidently.
Use diameter confidently.
Use circumference confidently.
Use area confidently.
Success checklist
✓I can explain what circles means.
✓I can choose a suitable method without being told.
✓I can show clear working and check my answer.
Worked example
A triangle has angles 52° and 68°. Find the third angle.
Step 1
Angles in a triangle add to 180°.
Step 2
52° + 68° = 120°.
Step 3
180° - 120° = 60°.
Answer
60°
Quick practice
Question 1
Find the missing angle on a straight line when one angle is 73°.
Question 2
Find the area of a triangle with base 8 cm and height 5 cm.
Question 3
Find the hypotenuse when the shorter sides are 6 cm and 8 cm.
Related resources
These are linked to the wider Geometry topic for now.