r = known radius x = known arc length --------------------------- C (circumference of circle) = 2 * PI * r A (angle of chord in degrees) = x / C * 360 L (length of chord) = r * sin(A/2) * 2
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There are a couple of different ways of finding the length of the chord of a circle. Probably the best is what is called the half angle formula.
It depends on what information you have: radius, diameter, lengths of tangents from a point outside the circle, length of chord and its distance from the centre, etc. Also, the term is circumference, not circumfrence.
The solution depends on the information supplied. Basically, you find the area of the sector containing the segment and then deduct the area of the triangle formed by the chord and the two radii enclosing the sector. If you are given the radius(r) of the circle and the height(h) then construct a radius that is perpendicular to and bisects the chord. This will create two congruent triangles which together form the main triangle. Using Pythagoras enables the half-chord length to be calculated as the hypotenuse is r and the height (also the length of the third side) is r-h. With this information the full chord length can be established and thus the area of the main triangle. Using sine or cosine methods enables the sector angle at the centre to be calculated and thus the sector area. Simple subtraction produces the area of the segment. If you are given the radius and the chord(c) length then the construction referred to above enables the height of the main triangle to be calculated and a similar process will generate the area of that triangle and the sector area. This, in turn, will enable the segment area to be determined.
you will need to know the angle subtended by the arc; arc length = radius x angle in radians
The area of a sector of a circle with radius 12 and arc length 10pi is: 188.5 square units.