Question

in the rhombus ABCD, AB=e, BC=f, triangle DAB=theta , theta does not equal to 90 degrees, absolute vale of e=1
which could be correct for the above rhombus description:
1)e*f=cos(180-0)
2)e*f does not equal zero
3)e*f=Cos(theta)
4)e*e=f*f
thanks in advance