Question

Rombul ABCD are m(<abc)=120grade si perimetrul egal cu 36 cm.Lungimea diagonalei BD este egala cu...?

Answer 1

$P_{romb}=4l=36cm \\ l=36:4 \\ l=9cm \\ AB=BC-CD=AD=9cm$ 
<ABD=<ABC / 2 = 60*
<ADB=<ABC / 2 = 60*
Deci ΔABD este echilateral, AB=AD=BD=9cm