Question

In a right-angled triangle $ABC$, if angle $B=90°$, $BC=3$$cm$ and $AC=5cm$, then the length of side $AB$ is ___________

• A. $3cm$
• B. $4cm$
• C. $5cm$
• D. $6cm$

Answer 1

The correct option is B

$4cm$

Find the length of the side AB

$∆ABC$ is a right angle triangle at $B$, $BC=3$$cm$ and $AC=5cm$,

From Pythagoras theorem,

$\Rightarrow A{C}^2=A{B}^2+B{C}^2$

$$\begin{gathered} \Rightarrow 5^2=A{B}^2+3^2 \\ \Rightarrow A{B}^2=5^2-3^2 \\ \Rightarrow AB=\sqrt{16} \\ \Rightarrow AB=4cm \end{gathered}$$

Hence, the length of the side $AB$is $4cm$.