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Question
Use the information given in the following figure to find the value of x.

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Solution
Take A, B, C, D as the vertices of Quadrilateral and BA is produced to E (say).
Since ∠EAD = 70°
∴ ∠DAB = 180° – 70°= 110° [EAB is a straight line and AD stands on it ∠EAD+ ∠DAB = 180°]
∴ 110° + 80° + 56° + 3x – 6° = 360°
[∵ sum of interior angles of a quadrilateral = 360°]
∴ 3x = 360° – 110° – 80° – 56° + 6°
3x = 360° – 240° = 120°
∴ x = 40°
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