MCQ
Mark $(\checkmark)$ against the correct answer.In the given figure, $\text{AB}\parallel\text{CD,}\angle\text{OAB}=150^\circ$ and $\angle\text{OCD}=120^\circ.$ The $\angle\text{AOC}={}?$
  • A
    $80^\circ$
  • $90^\circ$
  • C
    $70^\circ$
  • D
    $100^\circ$

Answer

Correct option: B.
$90^\circ$


In the figure, $\text{AB}\parallel\text{CD}$
$\angle\text{OAB}=150^\circ,\angle\text{OCD}=120^\circ$
From $O$, draw $\text{OE}\parallel\text{AB}$ or $CD$
$\text{AB}\parallel\text{DE}$
$\angle\text{OAB}+\angle\text{AOE}=180^\circ$
$\Rightarrow150^\circ+\angle\text{AOE}=180^\circ$
$\Rightarrow\angle\text{AOE}=180^\circ-150^\circ=30^\circ$
Similarly $\text{DE}\parallel\text{CD}$
$\Rightarrow\angle\text{EOC}+\angle\text{OCD}=180^\circ$
$\Rightarrow\angle\text{EOC}+120^\circ=180^\circ$
$\Rightarrow\angle\text{EOC}=180^\circ-120^\circ=60^\circ$
Now $\angle\text{AOC}=\angle\text{AOE}+\angle\text{EOC}$
$=30^\circ+60^\circ=90^\circ$

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