ABCD = dreptunghi
AB = 3 m AC =diagonala = ipotenuza in triunghiul ABC =5 m
AC ^2 =AB ^2 +BC ^2
5^2 =3^2 +BC ^2
BC ^ =5^2-3^2
BC ^2 =25-9
BC ^2 =16
BC =4 m
S podelei =3*4 =12m ^2 =12*10^2*2 =12*10^4 =12*10000 =120000 cm ^2
S placii =20*20 =40 cm^2
120000 :40 =3000 placi