AB=[tex]AB = \sqrt{ (-a-0)^{2}+ (3-8)^{2} }
\\ 13=\sqrt{ (-a-0)^{2}+ (3-8)^{2} }
\\ 13= \sqrt{ (-a)^{2}+ (-5)^{2} }
\\ 13= \sqrt{ a^{2} +25} / ()^2 - ridicam la patrat \\
169= a^{2} +25
\\ a^{2} +25=169 \\
a^{2}=169-25 \\
a^{2}=144 \\
a= \sqrt{144} \\ a=12
[/tex]
