The Figure shows a right triangle ABC at B (with green colour ) , and two blue lunes.The outside of each lune is a semicircle and the inside of each lune is part of the circle passing through the points A,B and C,(circumcircle of ABC). if AB = 8 and BC = 6,find the area of the two blue lunes ?
Definition of lune : A crescent-shaped figure formed on a sphere or plane by two arcs intersecting at two points.
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using The Pythagorean Theorem we can prove that : the area of the semicircle on AC = the sum of areas of the semicircles on AB and BC. ( By the way, this can be considered as an other extension of the Pythagorean Theorem).
Therefore ; the area of the semicircle on AC = the green area + the white area.
the sum of areas of the semicircles on AB and BC = the blue area + the white area
so far , the blue area = the green area = 24
AC is the diameter of the semi-circle formed by arcs AB and BC, given the theorem that any triangle with a base as the diameter of a circle will form a right angled triangle.
Area of the white portion = Area of the semi-circle mentioned above - Area of triangle ABC
= π x ( A C / 2 ) 2 - (0.5 x AB x BC)
Given A C 2 = B C 2 + A B 2
= π x [ ( B C / 2 ) 2 + ( A B / 2 ) 2 ] - (0.5 x AB x BC) ... (1)
Area of the semi-circles formed by the two lunes = π x [ ( B C / 2 ) 2 + ( A B / 2 ) 2 ] ... (2)
Required area of the two blue lines = (2) - (1) = (0.5 x AB x BC) = 0.5 x 6 x 8 = 24 square units
The area of the two blue lunes is equal to the area of the green triangle.
thats correct
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the above is hippocrates theorem
the below is proof