MCQ
In Fig. if $AB || CD,$ then $x =$
  • A
    $32$
  • $42$
  • C
    $52$
  • D
    $31$

Answer

Correct option: B.
$42$

Construction: Draw a line $PQ$ parallel to $AB$ which is also parallel to $CD$
$\angle \text{CDP}+\text{Reflex}\angle \text{CDP}=360^\circ$ [Complete angle]
$\therefore \text{CDP}+249^\circ=360^\circ$
$\Rightarrow \angle \text{CDP}=111^\circ$
Since, $PQ || AB$
$\therefore \angle \text{BAP}=\angle \text{APQ}$ [Alternate angles]
$\Rightarrow \angle \text{BAP}=28^\circ$
Now, $\angle \text{APQ}+\angle \text{QPD}=\angle \text{APD}$
$\Rightarrow 28^\circ+\angle \text{QPD}=(2\text{x}+13)^\circ$
$\Rightarrow \angle \text{QPD}=(2\text{x}+13)^\circ-28^\circ$
Since, $PQ || CD$
$\therefore \angle \text{QPD}+\angle \text{CDP}=180^\circ$ [Angles on the same side of a transversal line are supplementary]
$\Rightarrow (2\text{x}+13)^\circ-286\circ+111^\circ=180^\circ$
$\Rightarrow 2\text{x}+13-28+111=180$
$\Rightarrow 2\text{x}=84$
$\Rightarrow \text{x}=42$
Hence, the correct answer is option $(b).$

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