In order to calculate the value of 'a', we can use the Pythagorean theorem, where the hypotenuse squared is equal the sum of each leg squared:
[tex]h^2=l^2_1+l^2_2[/tex]
So if the hypotenuse is 12 and the legs are 9 and 'a', we have:
[tex]\begin{gathered} 12^2=9^2+a^2 \\ 144=81+a^2 \\ a^2=144-81 \\ a^2=63 \\ a=\sqrt[]{63} \end{gathered}[/tex]
So the number beneath the radical symbol is 63.
