11)
From the diagram above, using Pythagoras theorem
[tex]\begin{gathered} x^2=12^2-y^2\text{ ---------(1)} \\ \text{That is considering the big triangle ABC} \end{gathered}[/tex][tex]\begin{gathered} x^2=3^2+z^2 \\ \text{That is considering the first small triangle} \end{gathered}[/tex]
