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Razz KH Pandey

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· 1 Months ago

1. In square, diagonals cross each other at 90 degree.
2. How can any angle be 60 degree in a square.

Question:
ABCD is a square in which ∆OBC is an equilateral triangle, then find ∠ DOA.


Options:
A) 60° 
B) 45°
C) 150°
D) 90°
Solution:

Ans.(c)

        According to the question,

∠ BCD = 90°,

∠OBA =  ∠DCO = 90° – 60° = 30°

In ∆ OBA, 

∵ OB = AB

∴ ∠BOA = ∠BAO = \(\cfrac{180^0-30^0}{2}=75^0\)

Similarly,  in ∆ COD;

∠COD = ∠ODC = 75o

∴ ∠ DOA = 360o – 75o –  75o –  60o

=  ∠ DOA = 150o

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