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indrayani bargaje Grade: 10
         ABCD is a cyclic trapezium where AB||CD. if AB=4, AD=5, BD=7, find CD 
6 years ago

Answers : (2)

Harshit Kumar
15 Points
										

The answer is CD=6. 


Solution: draw BE parallel to AD such that BE=5 and DE=4. Let CE=x. 


then, let angle BEC=Z


so, angle ADE and angle BCD are also Z(corresponding angles and cyclic trapezium).


From triangles BED and BEC, 


cos 180-z=-cos z=(4^2+5^2-7^2)/2.4.5=-(5^2+x^2-5^2)/2.5.x


                             triangle BED                   Triangle BEC


on solving we get x=2 . so, CD=4+X=6.

6 years ago
indrayani bargaje
33 Points
										

thankyou so much!!!


 


but i didnt get why you took 


cos z=(4^2+5^2-7^2)/2.4.5=-(5^2+x^2-5^2)/2.5.x


                             triangle BED                   Triangle BEC


 


i think basically i donno cos funcn in obtuse triangle

6 years ago
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