Gujarat BoardEnglish MediumSTD 9MathsCircles [NEW]4 Marks
Question
ABCD is a cyclic trapezium with AD || BC. If $\angle\text{B}=70^\circ,$determine other three angles of the trapezium.
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Answer
We have ABCD is a cyclic trapezium with AD || BC and $\angle\text{B}=70^\circ.$ Since, ABCD is a cyclic quadrilateral Then, $\angle\text{B}+\angle\text{D}=180^\circ$ $\Rightarrow70^\circ+\angle\text{D}=180^\circ$ $\Rightarrow\angle\text{D}=180^\circ-70^\circ=110^\circ$ Since, AD || BC Then, $\angle\text{A}+\angle\text{B}=180^\circ$ [Co-interior angles] $\Rightarrow\angle\text{A}+70^\circ=180^\circ$ $\Rightarrow\angle\text{A}=180^\circ-70^\circ=110^\circ$ Since, ABCD is a cyclic quadrilateral Then, $\angle\text{A}+\angle\text{C}=180^\circ$ $\Rightarrow110^\circ+\angle\text{C}=180^\circ$
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