[tex]\displaystyle \bf\\
A_{\boxed{~}} = l \times L = 65 \times 84~~~\text{ (Nu efectuam calculul in acest moment)}\\\\
A_{\Delta} = \frac{c_1 \times c_2 }{2} = \frac{AB \times AC }{2} \\\text{unde }c_1=AB~si~c_2 =AC\text{ sunt catetele triunghiului, iar } AB = 42~m.\\\\
\text{Scriem ecuatia: }\\
A_{\boxed{~}}=A_{\Delta} \\\\
l \times L = \frac{AB \times AC }{2} \\\\
65 \times 84 = \frac{42 \times AC }{2}~~~~~\text{unde AC este necunoscuta in ecuatie.}
[/tex]
[tex]\displaystyle \bf\\
Rezolvare:\\\\
65 \times 84 = \frac{42 \times AC }{2}~~~\Big|~\times 2\\\\
65 \times 84 \times 2 = 42 \times AC\\\\
AC = \frac{65 \times 84 \times 2}{42} = 65 \times 2 \times 2 = 130 \times 2 = \boxed{260 m}[/tex]