`angle1 +angle4 =180^@` (L.P.A.) ......(1)

`angle 2+angle3 =180^@` ........(2)

(sum of opposite of a cyclic quadrilateral is `180^@`)

`therefore` From (1) and (2), we get

`angle1 +angle4 =angle2 +anlge3` ......(3)

But (opposite angles of a parallelogram )

`therefore` From (3) and (4) ,

`angle1 +angle4 =angle2 +angle4`

`rArrangle1 =angle2`

`rArrAE=AD" "(because" sides opposite to equal angles are equal")`