Answer 1

Let the four angle of a quadrilateral in AP.be a, `a+20°, a+40° and a+60°`

`∴ a+(a+20°)+(a+40°)+(a+60°)=360°` .............[Angle sum property]`

`⇒ 4a+120°=360°`

`⇒4a=240°`

`⇒a=60°`           ...................(1)

Thus, angles of a quarilateral are=`a,a+20°, a+40° and 60°`

                                               ` = 60°,80°,100° and 120°`