Question

if from an external point B of a circle with centre O, two tangents BC and BD are drawn such that DBC=120°,prove that DB+BC=BO, i.e.,BO=2BC

Answer 1

ΔOBC and ΔOBD are congurent by RHS rule
so angle OBC and angle OBD are equal by CPCT
therefore angle OBC=angle OBD =60°
In triangle OBC,
cos 60°=BC/OB
1/2=BC/OB
OB=2BC
hence proved

Answer 2

here is the answer...