English

BEC is an equilateral triangle inside the square ABCD. The value of angle ECD is ______.

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Question

BEC is an equilateral triangle inside the square ABCD. The value of angle ECD is ______.

Options

  • 60°

  • 30°

  • 75°

  • 45°

MCQ
Fill in the Blanks
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Solution

BEC is an equilateral triangle inside the square ABCD. The value of angle ECD is 30°.

Explanation:

Since ABCD is a square, each of its interior angles is 90°, meaning ∠DCB = 90°. Because ΔBEC is an equilateral triangle, its interior angle ∠ECB = 60°. Therefore, the value of ∠ECD is calculated as:

∠ECD = ∠DCB − ∠ECB = 90° − 60° = 30°

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Chapter 13: Rectilinear Figures [Quadrilaterals: Parallelogram, Rectangle, Rhombus, Square and Trapezium] - Exercise 13 (C) [Page 203]

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Selina Concise Mathematics [English] Class 9 ICSE
Chapter 13 Rectilinear Figures [Quadrilaterals: Parallelogram, Rectangle, Rhombus, Square and Trapezium]
Exercise 13 (C) | Q 1. (e) | Page 203
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