MCQ
Mark $(\checkmark)$ against the correct answer. In $\triangle\text{ABC},\angle\text{B}=90^\circ, AB = 5\ cm$ and $AC = 13\ cm.$ Then, $BC =?$
​​​​​​​
  • A
    $8\ cm.$
  • B
    $18\ cm.$
  • $12\ cm.$
  • D
    None of these.

Answer

Correct option: C.
$12\ cm.$

 $\text { In } \triangle \mathrm{ABC}, \angle \mathrm{B}=90^{\circ}$
$\text { But } A C^2=\mathrm{AB}^2+\mathrm{BC}^2 \text { (By Pythagoras Theoram) }$
$\Rightarrow(13)^2=(5)^2+\mathrm{BC}^2$
$\Rightarrow 169=25+\mathrm{BC}^2$
$\Rightarrow B C^2=169-25=144=(12)^2$
$\mathrm{BC}=12 \mathrm{~cm}$

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