AB and BC are two equal chords of a circle of length cm each. If radius of the circle is 5 cm, find the length of the chord AC.
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Let O be the center of the circle with radius equal to 5 and with O B ⊥ A C intersecting at point D . Point D divides O B into the lengths: O D = y , D B = 5 − y , and it also bisects the chord A C into: A D = D C = x . Focusing on the two right triangles △ O D C and △ B D C , we have the following Pythagorean relationships:
x 2 + y 2 = 5 2 (for △ O D C ),
x 2 + ( 5 − y ) 2 = ( 2 5 ) 2 (for △ B D C )
which yield: x = 4 , y = 3 . The length of chord A C is just equal to ∣ A C ∣ = 2 x = 2 ( 4 ) = 8 .