The line segment AB intersects the straight line CD at B; AB will be smallest when  is

An interior angle of a regular polygon is 5 times its exterior angle. Then the number of sides of the polygon is

• 14

• 16

• 12

• 18

3.

In a triangle ABC,
, then ∠B is

• 50°

• 80°

• 40°

• 60°

The measure of an angle whose supplement is three times as large as its complement, is

• 60°

• 75°

• 30°

• 45°