Step  1: Draw a imaginary diagram according to the question

            NOTE: Since ABCD is a parallelogram,

                        AB = CD ..............(1)

                        BC = AD ................(2)

Step 2: Mark the circle touching points with the sides of the parallelogram.

                (S, P, Q, and R tangencies )  

Step 3: Observe the figure and Write the equal lengths

          NOTE: Lengths of tangents from an external points are equal.

            EXAMPLE:    DR = DS (Tangents on the circle from point D)

                                  CR = CQ (Tangents on the circle from point C)

                                  BP = BQ (Tangents on the circle from point B)

                                  AP = AS (Tangents on the circle from point A)

Step 4: Adding all these equations, (Obtained in step 3)

            EXAMPLE: DR + CR + BP + AP = DS + CQ + BQ + AS

                              (DR + CR) + (BP + AP) = (DS + AS) + (CQ + BQ)

                                    CD + AB = AD + BC

Step 5: Putting the values of equations (1) and (2) in the equation obtained in step 3, (See the step 1 for Eq (1)&(2))

              EXAMPLE:      2AB = 2BC

                                        AB = BC …......(3)

Step 6:  Compare equation 1, 2 and 3 (See step 1 and step  5)

            NOTE: All the sides of the parallelogram are equal so, it is a rhombus

              EXAMPLE: AB = BC = CD = DA

                                Hence, ABCD is a rhombus.