Question

in figure,two chords AB and CD intersect at O. if OA=8cm, OC=4cm and OD=6cm then OB is?

Answer 1

From intersecting chords theorem, the product of the segments of chords are equal :
$OB\times~OA~=~OC\times~OD$

Plug the given values and solve $OB$ 
$OB\times 8~=~4\times 6\\OB=3$

Answer 2

6×4=ob×8 24=ob×8 OB=24/8=3 Therefore the answer is 3