notam rombul cu ABCD
AC=diagonala mica=13
in triunghiul ADC
AD=DC
inaltimea AF dusa din A _I_ DC
h=AF=12
FC=√(AC²-AF²)=√(13²-12²)=√(169-144)=√25=5
AD²=DC²
DC²=AF²+DF²
DC²=12²+(DC-5)²
DC²=144+DC²-10DC+25
DC²=169+DC²-10DC
10DC=169
DC=169:10=16,9 cm
Aria = 16,9x12=202,8cm²
