Gujarat BoardEnglish MediumSTD 8MATHSUnderstanding Quadrilaterals and Practical Geometry2 Marks
Question
In parallelogram $ABCD$, find $\angle\text{B}.\ \angle\text{C}\ \text{and}\angle\text{D}.$
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Answer
In a parallelogram, the opposite angles are equal, therefore $\angle\text{C}=\angle\text{A}=80^\circ$ Also, adjacent angles are supplementary.
$\therefore\angle\text{A}+\angle\text{B}=180^\circ$
$\Rightarrow80+\angle\text{B}=180^\circ$
$\Rightarrow\angle\text{B}=180^\circ-80^\circ=100^\circ$
Now, $\angle\text{B}=\angle\text{D}=100^\circ$
$\therefore\angle\text{D}=100^\circ.$
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