Parts of a circle
A line segment that goes from one side of the circle to the centre.
Radius
What fraction of a circle do I have if I have a sector with an angle of 90 degrees?
90/360 or 1/4
If the radius is 7cm, what is the diameter?
14cm
What's the formula for finding the length of the circumference?
C = 𝛑d or C = 2𝛑r
What's the length of the curved section (arc) of a sector with diameter 4m and angle 50°?
50/360 × 𝛑 × 4 = 1.75m
A line that goes from one side of the circle to the other and passes through the centre.
Diameter
What fraction of a circle do I have if I have a sector with an angle of 180 degrees?
180/360 or 1/2
If the radius is 93cm what is the diameter?
186cm
What's the circumference of a circle with diameter 3cm? (2 decimal places)
𝛑 × 3 = 9.42cm
What's the length of the curved section (arc) of a sector with diameter 7m and angle 120°?
120/360 × 𝛑 × 7 = 7.33m
The distance around the circle
Circumference
What fraction of a circle do I have if I have a sector with an angle of 270 degrees?
270/360 or 3/4
If the diameter is 10cm, what is the radius?
5cm
What's the circumference of a circle with diameter 13cm? (2 decimal places)
𝛑 × 13 = 40.84cm
What's the length of the curved section (arc) of a sector with diameter 10m and angle 72°?
72/360 × 𝛑 × 10 = 6.28m
A line that goes from one side of the circle to the other but might not go through the centre
Chord
What fraction of a circle do I have if I have a sector with an angle of 120 degrees?
120/360 or 1/3
If the diameter is 38cm, what is the radius?
19cm
What's the circumference of a circle with radius 2cm? (2 decimal places)
𝛑 × 2 × 2 = 12.57cm
What's the length of the curved section (arc) of a sector with radius 2m and angle 60°?
If radius is 2m, diameter is 4m
60/360 × 𝛑 × 4 = 2.09m
Half of the diameter
Radius
What fraction of a circle do I have if I have a sector with an angle of 144 degrees?
144/360 or 2/5
If you know how long the radius is, what do you do to find the diameter?
Double the radius; times the radius by 2
What's the circumference of a circle with radius 14cm? (2 decimal places)
𝛑 × 2 × 14 = 87.96cm
What's the length of the curved section (arc) of a sector with radius 22m and angle 300°?
If radius is 22m, diameter is 44m
300/360 × 𝛑 × 44 = 115.19m