in ascending to a higher altitude,the segment AB of an airplane wing makes an angle of 20 degree.for such a conditions to exist, the force on the wing should be 12,000 newton perpendicular to AB. what is the lift force and drag force?

Vertical: 12,000 cos 20

Drag: 12,000 sin 20 PLUS additional drag due to the drag coefficient, which they should have specified.

The net force on a wing is not perpendicular to the wing, but IS mostly in that direction. There is always a backwards component, given by the drag coefficient. The question oversimplifies the situation.