Question

Fie ABCD un paralelogram.Demonstrati ca AB•AD+BA•BC=0.(Vectori) AJUTOR!!!!!​

Answer 1

$\it \overline{BC}=\overline{AD}\\ \\ \overline{BA}\cdot BC=-AB\cdot AD \Rightarrow \overline{AB}\cdot\overline{AD}+\overline{BA}\cdot \overline{BC}=\overline{AB}\cdot\overline{AD}-\overline{AB}\cdot\overline{AD}=\overrightarrow{0}$