JEE Advance - Mathematics (2000 - No. 7)

Let $${C_1}$$ and $${C_2}$$ be respectively, the parabolas $${x^2} = y - 1$$ and $${y^2} = x - 1$$. Let $$P$$ be any point on $${C_1}$$ and $$Q$$ be any point on $${C_2}$$. Let $${P_1}$$ and $${Q_1}$$ be the reflections of $$P$$ and $$Q$$, respectively, with respect to the line $$y=x$$. Prove that $${P_1}$$ lies on $${C_2}$$, $${Q_1}$$ lies on $${C_1}$$ and $$PQ \ge $$ min $$\left\{ {P{P_1},Q{Q_1}} \right\}$$. Hence or otherwise determine points $${P_0}$$ and $${Q_0}$$ on the parabolas $${C_1}$$ and $${C_2}$$ respectively such that $${P_0}{Q_0} \le PQ$$ for all pairs of points $$(P,Q)$$ with $$P$$ on $${C_1}$$ and $$Q$$ on $${C_2}$$.
$$P_0 = (1, 2), Q_0 = (2, 1)$$
$$P_0 = (0, 1), Q_0 = (1, 0)$$
$$P_0 = (-1, 2), Q_0 = (2, -1)$$
$$P_0 = (1, 0), Q_0 = (0, 1)$$
$$P_0 = (2, 1), Q_0 = (1, 2)$$

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