"ABпараллельнаСD.OC:OA=7:3.НайтиOD:OB"

OD:OB = 7:3

To find the ratio OD:OB, we can use the property of parallel lines.

Since AB is parallel to CD, we can use the intercept theorem. According to the intercept theorem, if a line is parallel to one side of a triangle and intersects the other two sides, it divides those sides proportionally.

In this case, OC intersects AB at point O and divides it into two segments: OA and OB.

Given that OC:OA = 7:3, we can conclude that OD:OB will also be in the ratio of 7:3.

Hence, the ratio OD:OB is 7:3.