Find the area of the rhombus ABCD, if the angle B is 60 °, the diagonal AC is 8.5 cm.

Let’s find the area of the rhombus ABCD. Where the angle B is 60 °, let the O be the intersection point of the diagonals, the AC diagonal is 8.5 cm from this it follows that CO-8.5: 2 = 4.25.
Consider the BOS triangle
Angle B = 30 ’, leg BC = 4.25 x 2 = 8.5 (since the leg lying opposite an angle of 30’ degrees is equal to half of the hypotenuse)
The area of the rhombus is 8.5 ^ 2 = 72.25