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In the given figure, ABCD is an isosceles trapezium in which ∠CDA = 2x° and ∠BAD = 3x°. Find all the angles of the trapezium.

In the given figure, ABCD is an isosceles trapezium in which ∠CDA = 2x° and ∠BAD = 3x°. Find all the angles of the trapezium. Quadrilaterals, R.S. Aggarwal Mathematics Solutions ICSE Class 9.

Rectilinear Figures

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Answer

We know that,

Sum of adjacent co-interior angles of a trapezium = 180°

∴ ∠A + ∠D = 180°

⇒ 3x + 2x = 180°

⇒ 5x = 180°

⇒ x = 180°5\dfrac{180°}{5}

⇒ x = 36°.

∠A = 3x = 3(36°) = 108°

∠D = 2x = 2(36°) = 72°

∠B = ∠A = 108° [∵ base angles of an isosceles trapezium are equal]

∠C = ∠D = 72° [∵ base angles of an isosceles trapezium are equal]

Hence, ∠A = 108°, ∠C = 72°, ∠B = 108° and ∠D = 72°.

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