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In the given figure, ABCD is a cyclic quadrilateral. AF is drawn parallel to CB and DA is produced to point E. If ∠ADC = 92°, ∠FAE = 20°; determine ∠BCD. Give reason in support of your answer. - Mathematics

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Question

In the given figure, ABCD is a cyclic quadrilateral. AF is drawn parallel to CB and DA is produced to point E. If ∠ADC = 92°, ∠FAE = 20°; determine ∠BCD. Give reason in support of your answer.

Sum

Solution


In cyclic quad. ABCD,

AF || CB and DA is produced to E such that ∠ADC = 92° and ∠FAE = 20°

Now, we need to find the measure of ∠BCD

In cyclic quad. ABCD,

`=>` ∠B + ∠D = 180°

`=>` ∠B + 92° = 180°

`=>` ∠B = 180° – 92°

`=>` ∠B = 88°

Since AF || CB, ∠FAB = ∠B = 88°

But, ∠FAE = 20°   ...[Given]

Ext. ∠BAE = ∠BAF + ∠FAE

= 88° + 20° 

= 108°

But, Ext. ∠BAE = ∠BCD

∴ ∠BCD = 108°

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Chapter 17: Circles - Exercise 17 (C) [Page 266]

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Selina Mathematics [English] Class 10 ICSE
Chapter 17 Circles
Exercise 17 (C) | Q 8 | Page 266
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