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The angle between two altitudes of a parallelogram through the vertex of an obtuse angle of the parallelogram is 60º. Find the angles of the parallelogram. - Mathematics

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Question

The angle between two altitudes of a parallelogram through the vertex of an obtuse angle of the parallelogram is 60º. Find the angles of the parallelogram.

Sum

Solution

In quadrilateral DPBQ:


∠1 + ∠2 + ∠B + ∠3 = 360°   ...[Angle sum property of quadrilateral]

60° + 90° + ∠B + 90° = 360°

∠B + 240° = 360°

∠B = 360° – 240°

∠B = 120°

Since, ∠ADC = ∠B = 120°  ...[Opposite angles of a parallelogram are equal]

∠A + ∠B = 180°  ...[Sum of consecutive interior angle is 180°]

∠A + 120° = 180°

∠A = 180° – 120°

∠A = 60°

So, ∠C = ∠A = 60°   ...[Opposite angle of a parallelogram are equal]

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Chapter 8: Quadrilaterals - Exercise 8.3 [Page 78]

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NCERT Exemplar Mathematics [English] Class 9
Chapter 8 Quadrilaterals
Exercise 8.3 | Q 3. | Page 78

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