Please solve q 9 ?

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1 Answer
CW
May 6, 2018

#angleBDE=30^@#

Explanation:

enter image source here
As shown in the figure, #ABCD# is a square. Two circles with center at #B and C#, respectively, meet at #E#,
let #r# be the side of the square and the radius of the circles,
#=> BE=BC=CE=r#,
#=> DeltaBEC# is equilateral,
#=> angleBCE=60^@#,
recall that the angle subtended by an arc at the center of a circle is twice the angle subtended by the same arc at the circumference,
#=> angleBCE=2*angleBDE#,
#=> angleBDE=(angleBCE)/2=60/2=30^@#

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