The circle
If you know one measurement of a circle, you know them all. Enter the one you have and get the rest — plus the arc and the area of a sector.
Your numbers
Answer
The radius
5cm
Diameter
10cm
Circumference
31.4159cm
Area
78.5398cm²
Arc length (90°)
7.854cm
Area of sector (90°)
19.635cm²
How to work it out
- 1r = d / 2 = 10 / 2 = 5 cm
- 2O = 2 · π · r = 31.4159 cm
- 3A = π · r² = π · 5² = 78.5398 cm²
- 4Arc = 90° / 360° · 31.4159 = 7.854 cm
- 5Crop = 90° / 360° · 78.5398 = 19.635 cm²
The formula
d = 2 · r
The diameter is twice the radius.
O = π · d = 2 · π · r
π (pi) ≈ 3.14159 — the ratio between circumference and diameter in every circle.
A = π · r²
bue = v/360 · O · udsnit = v/360 · A
A sector with the angle v is v/360 of the whole circle.
More: Geometry
- PythagorasFind the missing side of a right triangle — with a drawing and working.
- Area and perimeterRectangle, triangle, parallelogram, trapezoid and circle — area and perimeter.
- Volume and surface areaBox, cube, cylinder, cone, sphere and pyramid — also in litres.
- Right triangleSine, cosine and tangent: all sides and angles from two known values.
- AnglesThe third angle in a triangle and the angle sum of a polygon.
- Points in the coordinate systemDistance, midpoint and the line between two points — drawn in.