1) Show that quadrilateral ABCD can be inscribed in a circle iff and are supplementary.
2) Prove that a parallelogram having perpendicular diagonals is a rhombus.
3) Prove that a parallelogram with equal diagonals is a rectangle.
4) Show that the diagonals of an isosceles trapezoid are equal.
5) A straight line cuts two concentric circles in points A, B, C and D in that order. AE and BF are parallel chords, one in each circle. If CG is perpendicular to BF and DH is perpendicular to AE, prove that .
6) Construct triangle ABC, given angle A, side AC and the radius r of the inscribed circle. Justify your construction.
7) Let a triangle ABC be right angled at C. The internal bisectors of angle A and angle B meet BC and CA at P and Q respectively. M and N are the feet of the perpendiculars from P and Q to AB. Find angle MCN.
8) Three circles with radii , with . They are placed such that lies to the right of and touches it externally; lies to the right of and touches it externally. Further, there exist two straight lines each of which is a direct common tangent simultaneously to all the three circles. Find in terms of and .