→ → → →
AC=u+v= [6,5] to: |AC|= √62+52=...... BD=u−v=[4,−1] to |BD|= √42+(−1)2=...
|AB|=|DC|=|u|= √52+22=.... |AD|=|BC|=|v|=√12+32=...
Ob= 2|AB|+ 2|AD|=....