A = (10 x 10):2 =100:2=50(cm^2)
sau
[tex]diagonala\;patratului\;=l_{patrat}\cdot\sqrt2\\
\Rightarrow\;\;\;l\cdot\sqrt2=10\rightarrow\;\;l=\frac{10}{\sqrt2}=\frac{10\sqrt2}{2}=5\sqrt2(cm)\\
\Rightarrow\;\;\;\;A_{patrat}=l^2=(5\sqrt2)^2=25\cdot2=50(cm^2)[/tex]
