Aria unui triunghi = produsul a 2 laturi ori sinusul unghiului dintre ele,
totul supra 2.
.
[tex]\displaystyle\bf\\\text{Diagonala unui paralelogram, imparte paralelogramul}\\\text{in 2 triunghiuri congruente.}\\\\Calculam~aria~\Delta ABC.\\\\Aria_{\Delta ABC}=\frac{AB\times AC\times sin45}{2}=\frac{20\times 15\times \dfrac{\sqrt{2}}{2}}{2}=\\\\=\frac{10\times 15 \sqrt{2}}{2}=5\times 15 \sqrt{2}=75\sqrt{2}~cm^2\\\\Aria_{ABCD}=2\times Aria_{\Delta ABC}=2\times 75\sqrt{2}=150\sqrt{2}~cm^2\\\\\boxed{\bf Aria_{ABCD}=150\sqrt{2}~cm^2}\\\\Raspuns~corect~a).[/tex]
