Aparalelogram=48 cm²
diagonalele in paralelogram impart paralelogramul in triunghiuri cu arii egale
Atriunghi BOC= 48:4=12 cm²
AC ∩ DB ={O}
OC=12/2=6
OB=16/2=8
Atriunghiului COB= OB × OC ×sin (<COB) /2
12=8×6 ×sin (<COB)/2
24=48×sin (<COB)
sin (<COB)=24/48=1/2
m(<COB)=30°
