d- przekątna kwadratu
d=a\sqrt2
a)
d=2
a\sqrt2=2/:\sqrt2
a=\frac{2}{\sqrt2}*\frac{\sqrt2}{\sqrt2}=\frac{2\sqrt2}{2}=\sqrt2[cm]
P=a^2=(\sqrt2cm)^2=2cm^2
b)
d=10
a\sqrt2=10/:\sqrt2
a=\frac{10}{\sqrt2}*\frac{\sqrt2}{\sqrt2}=\frac{10\sqrt2}{2}=5\sqrt2[cm]
P=(5\sqrt2)^2=25*2=50[cm^2]
c)
d=3\sqrt2
a\sqrt2=3\sqrt2/:\sqrt2
a=3[cm]
P=3^2=9[cm^2]