Circle Theorems Calculator
Our free circle calculator solves circle theorems problems. Get worked examples, visual aids, and downloadable results.
Reviewed by Manoj Kumar, Mathematics Educator
Formula
Inscribed Angle = Central Angle / 2
The inscribed angle theorem states that an inscribed angle is half the central angle subtending the same arc. Related theorems cover tangent-radius perpendicularity, equal tangent lengths, chord-chord products, and cyclic quadrilateral angle sums.
Worked Examples
Example 1: Inscribed Angle from Central Angle
Problem:A circle has radius 10 and a central angle of 80 degrees. Find the inscribed angle, arc length, and chord length.
Solution:Radius r = 10, central angle = 80 degrees = 1.3963 radians\nInscribed angle = 80 / 2 = 40 degrees\nArc length = r * theta = 10 * 1.3963 = 13.963\nChord = 2r * sin(theta/2) = 20 * sin(40) = 20 * 0.6428 = 12.856\nPerpendicular distance from center to chord = sqrt(100 - 41.28) = 7.660
Result:Inscribed angle: 40 degrees | Arc: 13.963 | Chord: 12.856
Example 2: Tangent Length from External Point
Problem:Find the tangent length from a point 15 units from the center of a circle with radius 10.
Solution:Distance d = 15, radius r = 10\nTangent length = sqrt(d^2 - r^2) = sqrt(225 - 100) = sqrt(125) = 11.180\nAngle between tangent and line to center = arccos(r/d) = arccos(10/15) = 48.19 degrees\nPower of point = d^2 - r^2 = 225 - 100 = 125\nAngle between two tangents = 2 * arcsin(r/d) = 2 * arcsin(0.667) = 83.62 degrees
Result:Tangent length: 11.180 | External angle: 48.19 degrees | Power: 125
Frequently Asked Questions
How are intersecting chords related in a circle?
When two chords intersect inside a circle, the products of their segments are equal. If chord AB intersects chord CD at point P inside the circle, then AP times PB equals CP times PD. This is a special case of the power of a point theorem where the point lies inside the circle. For example, if one chord is divided into segments of length 3 and 8 by the intersection point, and the other chord has one segment of length 4, then the other segment must have length (3 times 8)/4 = 6. This relationship extends to secant lines from external points: if two secants from external point P intersect the circle at A, B and C, D respectively, then PA times PB equals PC times PD. These properties are useful in surveying and construction for indirect distance measurements.
How do circle theorems apply to real-world problem solving?
Circle theorems have extensive practical applications across many fields. In architecture, the inscribed angle theorem helps design arched windows and domed ceilings with precise angular relationships. In navigation, the angle in a semicircle theorem allows sailors to determine their position relative to two landmarks when the angle between them is 90 degrees. In engineering, tangent properties determine gear tooth profiles (involute gears), cam follower contact points, and pipe fitting angles. In computer graphics, circle theorems enable efficient algorithms for circle-circle and line-circle intersections used in collision detection and rendering. In optics, tangent lines to circular mirrors determine reflection paths. In sports analytics, the inscribed angle theorem helps analyze shooting angles in basketball and soccer goal scoring probabilities.
References
Reviewed by Manoj Kumar, Mathematics Educator · Editorial policy