Demand curve is the relationship between price and quantity of product. In perfect competition, the demand curve for the product by a firm is perfectly elastic at maket price.
PQ and RS are common tangents to two circles intersecting at A and B. AB, when produced both sides, meet the tangents PQ and RS at X and Y, respectively. If AB = 3 cm, XY = 5 cm, then PQ (in cm) will be