Question
The sides of a cyclic quadrilateral taken in an order are 15 cm, 21 cm, 18 cm and 20 cm. If one of its diagonals is 23 cm, then find the other diagonal.
(A) 48 cm, (B) 32 cm, (C) 26 cm (D) 30cm
solution
product of diagonals = sum of products of opposite sides
23*x= 270+420 = 690
x= 30
or
use Ptolemy theorem
((18*15) + (20*21))/23 = 30