ABCD is a rhombus whose side AB = 4 cm and ∠ABC = 120°,

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ABCD is a rhombus whose side AB = 4 cm and ∠ABC = 120°, then the length of diagonal BD is equal to :

According to question , we draw a figure of rhombus ABCD

Here , AB = 4 cm and ∠ABC = 120°
From ∆BOC,

cos 60° =	BO
	4

⇒ BO =	1	× 4 = 2 cm
	2

∴ BD = 2BO = 2 × 2 = 4 cm